The third seed started off slowly and dropped the first set to her fired-up opponent in just 35 minutes.
De Brito kept her composure to stay ahead, with Sharapova injuring her hip after falling heavily on three separate occasions.
The world number 131 held off a late fightback in the second set to claim a straight-sets victory, dumping out the 2004 champion in the process.
Look back at another early shock in this year's championships with Sports Mole's minute-by-minute commentary below.
3.55pmAfternoon Wimbledon fans. Thanks for sticking with Sports Mole for comprehensive live coverage from SW19, which continues with a second-round match featuring former champion Maria Sharapova.
3.58pmSharapova continues her campaign today on Court Two, where she will face Portuguese qualifier Michelle Larcher de Brito for the first time in her career. She possesses a shriek to match her famous Russian opponent, so expect the noise level to set new records in this one.
4.01pmSharapova may be slightly miffed with a rare appearance on Court Two this afternoon, but expect the world number three to punish her opponent with a professional display. De Brito has just one win in three attempts on the main tour this year, so this afternoon's match definitely represents a baptism of fire. She has reached the third round of a Grand Slam before though, at the French Open in 2009.
4.03pmThe women's draw has opened up a touch for Sharapova this afternoon, with potential semi-final opponent Victoria Azareknka withdrawing through injury. That should provide the Russian with a little extra incentive to win back her title this year, but first things first a tricky tie against unheralded De Brito, which is just about to get underway.
4.05pmDe Brito opens on serve and has a forehand to the baseline challenged by Sharapova with the very first point, not sure I've seen that before. A fruitless challenge though from the Russia, who responds by narrowly missing the line with an attempted backhand winner across court.
Sharapova *0-1 Larcher de BritoAn encouragingly comfortable early hold for De Brito, who benefits from a pair of unforced errors on Sharapova's forehand side. Expect those to become a rare occurrence as the world number three finds her feet in this match.
Sharapova 1-1* Larcher de BritoSharapova shows neat touch at the net to complete an opening hold to love, working behind a first serve that finds the line with power on more than once occasion. Ominous signs for De Brito, who will need to show similar strength on serve to have any chance in this match.
4.12pmThe first signs of strain on Larcher De Brito's serve, with a gutsy effort at the baseline not enough to ease ahead at deuce. Break point to Sharapova but the Portuguese youngster hangs on, sending a measured forehand down the line under pressure.
Sharapova *1-2 Larcher de BritoFine groundstrokes under considerable pressure sees Larcher de Brito keep this first set on serve. You feel that was an important hold for the underdog's confidence, showing surprising power to save break point. That high standard will need to be maintained though, with Sharapova back on serve after a change of ends.
4.17pmA lengthy and fierce baseline exchange sees Larcher de Brito triumph, smashing a forehand winner out of reatch at the baseline. Sharapova then volleys wide under little pressure at the net, giving her opponent a window of opportunity at 15-30.
Sharapova 1-3* Larcher de BritoBREAK! Well how about that, another perfectly timed forehand winner sees DE Brito take an early break. We may just have a match on our hands here, with the Portuguese qualifier deceiving her more experienced opponent with balance and poise at the baseline.
4.22pmMore like it from Sharapova and an instant response, with the world number three slamming a huge passing forehand into the corner. That well-timed strike puts De Brito under instant pressure at 30-30, but once again she responds with a deep backhand across court that gives her no chance of chasing the ball down.
Sharapova *1-4 Larcher de BritoSharapova walks back to her chair with shoulders slumped as she falls 4-1 behind, courtesy of another slick effort at the baseline from De Brito. Not sure if she can keep this ruthless streak up at both ends of the court, but the Russian definitely looks surprised at the resistance she is meeting in this first set.
4.28pmBREAK POINTS! A first double fault put Sharapova under further pressure on serve, with De Brito following that effort up with a backhand winner to push 15-40 ahead. The Russian uses a fierce serve to respond, quickly fighting back to deuce with relative ease.
Sharapova 2-4* Larcher de BritoOverdue aggression from Sharapova sees her claim a hard-fought hold, driving in quickly to finish things off with power at the net. All the pressure now falls on Larcher de Brito's ability to stay strong on serve, if she can the opening set awaits.
Sharapova *3-4 Larcher de BritoBREAK! A second double fault from Larcher de Brito sees her fall 15-40 behind on serve, with a ferocious baseline exchange enough for Sharapova to break back in the very next point. The noise levels are rising from both players after that battle, with Sharapova shrieking in trademark style after cancelling out that early break of serve.
4.35pmBREAK POINTS! What a magnificent response from Larcher de Brito, getting the better of a powerful baseline rally to earn three break points.
Sharapova 3-5* Larcher de BritoBREAK! You have to say that is quite magnificent from the Portuguese qualifier. A break to love is clinched by a massive forehand down the line and Sharapova is broken for the second time today. Larcher de Brito has earned the chance to serve for the opening set with confident play that belies her lowly ranking.
Sharapova *3-6 Larcher de BritoSET! Sharapova slips twice at the baseline and fails to recover, conceding cheap points in succession and with it the first set. The third seed has struggled to stamp her authority in this match, falling a set down in just 35 minutes to her relatively unknown opponent.
4.41pmLarcher de Brito has shown an aggression this afternoon that was completely unexpected. Sharapova has been known to start slowly in matches where she should win comfortably, with her troubles today largely coming on serve. De Brito hits hard and looks to be relishing the challenge of taking on a former champion on Court Two, starting the second set by winning the opening point against serve.
Sharapova 3-6 1-0* Larcher de BritoSharapova sums up her slack start by following an ace with a double fault, but still has enough to ease into the second set with an early hold. The Russian stares glaringly at a line judge after that game and looks in no mood to hang around this afternoon as she looks to mount a comeback.
Sharapova 3-6 *1-1 Larcher de BritoThree separate unforced errors crash into the net from Sharapova, allowing Larcher de Brito to level the second set with ease as she takes the hold. More aggression from the qualifier then sees her chase down a drop shot and she looks delighted with that effort, pumping her fist out to warm applause from a crowd enjoying every minute of this match.
4.48pmBREAK POINTS! Sharapova can't quite believe it as she falls 15-40 behind on serve, with Larcher de Brito scorching a blistering forehand pass across court to earn two break points. What a chance this is to claim an early advantage in the second set, with a lead already banked. Sharapova has little answer to the barrage coming her way this afternoon so far.
Sharapova 3-6 1-2* Larcher de BritoBREAK! An untimely double fault from Sharapova is not reversed by a hopeful challenge, giving her spirited opponent a vital break of serve. There has been no sign of a let up from the Portuguese number two today, with accurate shots coming in abundance from a player ranked 131 in the world. Quite incredible.
4.53pmFinally a couple of unforced errors creep in from Larcher de Brito at the baseline, allowing Sharapova to level up at 30-30 in. Another positive response from the qualifier sees a powerful first serve go unreturned.
Sharapova 3-6 *1-3 Larcher de BritoComposure and class from Larcher de Brito, swiftly shuffling across court to slam a forehand winner up the line. I keep waiting for a chink in the armour of the Portugese youngster and so does Sharapova, but right now you have her to make the favourite to go on and claim a breakthrough victory.
Sharapova 3-6 2-3* Larcher de BritoSharapova sends a hopeful forehand long and once again is under massive pressure on serve at 30-30. Just when she needs it the Russian produces a huge second serve, bouncing high out of her opponent's reach to earn the hold.
5.02pmA third slip from Sharapova sees the Russian slip and land in a very awkward position at the baseline, that fall almost made the Russian do the splits and she looks very upset with the surface. The umpire comes out of her chair to check the third seed is alright to continue, with play restarting after a short delay.
Sharapova 3-6 *2-4 Larcher de BritoNo mercy from Larcher de Brito as she takes a two-game lead in the second set, punishing Sharapova with a precise forehand deep into the far corner on two separate occasions. The Russian is making surprising errors and looks uncomfortable at the baseline, for fans of the third seed it's definitely time to anxious.
5.07pmTwo aces in a row help Sharapova earn easy points she desperately needs to draw level on serve at 30-30. A challenge from the Russian then goes her way at the baseline, giving her the chance to replay a point she initially looked destined to lose.
Sharapova 3-6 3-4* Larcher de BritoRaw power earns Sharapova a hold she simply had to claim to stay alive. The third seed has called for the trainer during a short break and appears to be in some discomfort with her hip. Her mood is not helped by a heated exchange with the officials over what clearly appears to be a slippery playing surface.
5.13pmSharapova takes a medical timeout as she leaves the court for treatment on her hip. Larcher de Brito must maintain concentration during this break and decides to practise her serve during the unwelcome interval.
5.16pmA restless crowd on Court Two fill the void with a Mexican wave, but when Sharapova returns focus will be vital from both players. A reminder that Larcher de Brito leads with a set and a break and stands just two games away from humbling the former champion this afternoon.
5.19pmLarcher de Brito picks up where she left off after a lengthy break, forcing an error from Sharapova at the baseline to go 30-15 ahead in this crucial game. The Russian shows no sign of injury and quickly responds, launching an awesome forehand winner across court.
5.21pmBREAK POINT! The longest rally of the match by quite some distance sees Sharapova's experience prevail to earn a break-point chance. She is unable to capitalise though, crashing a sloppy forehand return straight into the net under virtually no pressure.
Sharapova 3-6 *3-5 Larcher de BritoUnforced errors complete ruin Sharapova's earlier good work, with a silly effort on her forehand side flying wide. Larcher de Brito is pumped up and quickly moves to start the next game. Sharapova will now serve to stay in the championship, but starts with a disastrous double fault.
5.24pmA credible attempt at a forehand slice trickles past the line from Larcher de Brito, allowing Sharapova to take advantage and build a 40-15 lead with a serve of 106mph in the next point.
Sharapova 3-6 4-5* Larcher de BritoStill not completely comfortable from Sharapova, but power behind the first serve proves just enough to keep her alive in the match. All the pressure now falls on her 20-year-old opponent, who after a short break will serve to claim easily the biggest scalp of her career to date.
5.30pmA colossal first serve gets Larcher de Brito on the board in this vital game, but an unforced error on her forehand side helps Sharapova fight back at 30-30. Huge pressure on both players now.
5.32pmMATCH POINT! Staring at defeat Sharapova gets aggressive with a huge effort at the net, saving match point with a massive volley. Larcher de Brito is quickly given a second chance to close things out though, can she take it?
5.34pmMake that two match points saved for Sharapova now, with both players giving it everything as their powerful strokes are matched with huge screams. This vital game is deadlocked at deuce and could still go either way.
5.36pmBREAK POINT! Sharapova saves a third match point and keeps fighting back, getting the better of a baseline exchange that was gruelling to watch never mind play in.
Sharapova 3-6 4-6 Larcher de BritoGAME SET AND MATCH! At the fourth time of asking Larcher de Brito gets the job done, claiming a famous victory her play this afternoon richly deserved. Despair for Sharapova but the day belongs to the Portuguese qualifier, who gets a standing ovation from a delighted Court Two crowd.
5.40pmLarcher de Brito was utterly fearless in that second-round match, with the 20-year-old knocking out the 2004 Wimbledon champion in straight sets. Sharapova just never looked comfortable out there today, with her tournament ended abruptly as a result.
5.42pmSharapova took a few heavy falls in that match but in truth the third seed was well beaten. A lot has been made of the slippery courts at Wimbledon this year, with Sharapova the latest player to crash out on a quite remarkable third day of action at SW19.
5.46pmThat just about ends our coverage from Court Two this afternoon. Just to sum things up the world number 131 has just resoundingly beaten the four-time Grand Slam champion Sharapova in straight sets, quite incredible. Thanks for your time and enjoy the rest of today's action.