Crystal Palace pulled off one of the shocks of the season at Selhurst Park this afternoon, beating Premier League leaders Chelsea 1-0 to boost their survival hopes and damage the Blues' title aspirations.
Terry almost atoned for his own goal when he clipped the top of the bar at the other end, while Palace also came close to adding to their lead when Cameron Jerome struck the foot of the post.
Here, Sports Mole takes an in-depth look at a potentially pivotal afternoon in the Premier League season.
On target: 4
On target: 2
Was the result fair?
Yes. The stats may appear to favour Chelsea and the visitors certainly saw plenty of the ball - particularly after going behind - but Palace's defensive performance and all-round work rate was sensational as they nullified the Chelsea threat.
Having two thirds of the possession and 21 shots, yet only managing two on target, speaks volumes about how hard Chelsea found it to break down the stubborn rearguard action of Palace this afternoon. Yet it wasn't just in defence that Palace excelled as they also created far more clear-cut chances than their opponents.
As soon as Chelsea went behind they cranked up the pressure and were asking serious questions of the Palace defence. However, each time they had an answer and for a 10-minute spell in the second half that answer was to launch counter-attacks that often caught Chelsea short at the back.
Jose Mourinho may be wondering why his side struggled to create much on the back of such a comprehensive victory against Arsenal last week, but he need look no further than Palace's teamwork and desire. The stats make it look like a smash-and-grab victory, but Palace are fully deserving of all three points.
Crystal Palace's performance
Tony Pulis has enjoyed plenty of highs in his short Palace career so far, but this will be the best of the lot. His side, written off by the vast majority before the game, were superb this afternoon, stopping Chelsea playing their own game and enforcing their own style on the leaders.
The likes of Eden Hazard, Andre Schurrle and Frank Lampard were starved of the ball for much of the match as Palace's teamwork denied the creative trio any room to manoeuvre. The first half was an even affair short of clear chances, and that was largely down to the home side's tactics.
The second half saw a lot more goalscoring opportunities, but most of them fell the way of Palace. They should have added to their lead as they continually hit Chelsea on the counter, but the lack of cutting edge again threatened to undo their hard defensive work as they failed to kill Chelsea off.
However, they did manage to hold on for an unexpected and deserved three points, and if they put in seven more performances like that this season, then they will still be a Premier League side next year.
After recording their biggest win under manager Mourinho in their last match, the Blues will be wondering why they lacked such a cutting edge in front of goal today. Credit does have to go to Palace for their defensive performance, but with the quality of players at Chelsea's disposal, they should have been able to create more.
The Blues only really had two clear chances in the whole game, and a mixture of good defending and poor finishing prevented them from taking advantage of those. They struggled to dominate possession as they may have expected to and Palace were very much a match for them.
Their title challenge is by no means over, but such a result is very damaging and hands the initiative very much to Manchester City and, to a lesser extent, Liverpool. It is now two consecutive away defeats in the league for Mourinho's men, and he knows he can't afford another if they are to win the league.
Sports Mole's man of the match
Mile Jedinak: The man of the match was always going to come from the Palace side, but it is hard to pick out a single individual more deserving of the award than another as it was a fine team performance. Jedinak gets the nod for the crucial role he played protecting the back four from the likes of Hazard, Lampard, Schurrle and later Oscar. The midfield were always going to need to help the defence out today, and Jedinak was at the forefront of that happening.
This one has to go to Terry for his match-deciding and potentially season-defining own goal. The Chelsea skipper looked distraught as he nodded the ball past his own keeper under pressure from Joe Ledley from Joel Ward's cross. Petr Cech cannot be absolved of blame completely as he came off his line when the ball never looked like making it past Ledley and Terry, but the former England international has made that sort of clearance countless times in his career and will be disappointed to have turned it into his own net on this occasion.
Lee Mason was busy in a scrappy first half and had a number of penalty appeals to deal with. The most controversial of those was a tackle by Gary Cahill on Yannick Bolasie inside the box that could easily have been given. It looked like a good challenge at first glance, but the replays showed that the Chelsea man did not get much on the ball at all.
Crystal Palace: Palace will look to continue their newfound momentum when they travel to South Wales for a huge relegation battle against Cardiff City next Saturday.
Chelsea: Chelsea, meanwhile, must turn their attention to European matters as they face Paris Saint-Germain in the first leg of their Champions League quarter-final tie on Wednesday.