© Getty Images
Blues boss Guus Hiddink took no risks with his team selection, naming arguably a full-strength side with the exception of Thibaut Courtois and John Terry, who were both named on a bench that also included Ruben Loftus-Cheek.
Scunthorpe, on the other hand, only had 12 minutes of Premier League experience in their XI and that came from former West Bromwich Albion goalkeeper Luke Daniels. Luke Williams and Kevin van Veen were both bright for the visitors in the early exchanges and the League One outfit managed to restrict Chelsea to very little in the opening 10 minutes.
In the 13th minute, however, the home side were ahead when Scott Laird, under pressure from Diego Costa, could only turn a Branislav Ivanovic cross past his own goalkeeper from inside the box. Replays were inconclusive, but after much debate, Costa was credited with the first touch and therefore went down as the scorer.
The Blues came close to a second three minutes later, but Daniels kept out a Cesc Fabregas strike, before saving a thumping effort from Pedro. Oscar then curled one wide of the post as Scunthorpe struggled with 22 minutes on the clock.
A corner in the 27th minute provided Scunthorpe with their first sight of the Chelsea goal, but Stephen Dawson's thumping strike from close range was blocked by the head of Gary Cahill. Williams then found space outside the Chelsea box shortly after, but his low strike was saved by Asmir Begovic.
Scunthorpe actually ended the first period on top, with Williams taking advantage of a couple of defensive mistakes, but his best chance after driving into the Chelsea box was thwarted by a fine challenge from Kurt Zouma.
Willian, always so dangerous from free kicks, delivered a set piece towards the Scunthorpe box early in the second half, but Daniels was on hand to claim as the score remained 1-0 with 10 minutes of the second period played.
Shortly after, Scunthorpe had a strong penalty shout when Van Veen found down inside the box under pressure from Ramires, but the referee was not interested. That call spurred on the away side's supporters and as the match approached the hour, it was the third-tier outfit that looked most likely to score the game's second goal.
It was Chelsea that moved 2-0 ahead in the 68th minute, however, when Loftus-Cheek, who showed drive throughout the second period, converted a low cross from Cesar Azpilicueta.
Van Veen almost hit back for Scunthorpe moments later, but his free kick hit the side-netting, much to the disappointment of the away side's supporters, who saw the net move from the other side of the ground.
Jordan Clarke also came close to scoring for the away side in the latter stages, but his strike from a wide angle rattled the crossbar, before Neal Bishop squeezed one wide late on. It is Chelsea that progress into the fourth round and they will have their eye on an eighth FA Cup trophy this season.