Chelsea might almost feel like presenting Birmingham City with a sum of money to equal the gate receipts here at St Andrew's. This FA Cup replay, which takes them to a home tie with Leicester City, provided the visitors with a generous helping of normality after the sacking of André Villas-Boas.

There was a clean sheet, even if little effort was called for to secure it, and John Terry's knee injury is less severe than it seemed since he was on the bench here as an unused substitute. Although Juan Mata was to fail from the penalty spot, Chelsea had little to concern them.

The caretaker manager, Roberto Di Matteo, must have been eager to show that he could handle this assignment efficiently. An appointment will surely be made before long and it would help Di Matteo if he is seen as a trusty adviser to that newcomer. Complexities linger but they were invisible on Tuesday night. The game was mediocre at best and the goals were delayed until after the interval but there was nothing at all that preyed on Chelsea's nerves.

Birmingham were far from full strength and that was all the more dismaying when Chelsea felt no need to pick all of their high-profile figures from the outset. Frank Lampard, Didier Drogba and Michael Essien were named among the substitutes but that did not indicate demotion so much as Di Matteo's justified assumption that victory was well within reach of the line-up selected. Drogba was the one member of that trio not to take part eventually.

In any circumstances under any Chelsea manager, it would have made sense to conserve strength for the Premier League and that second leg with Napoli in a Champions League tie where they lag 3-1.

Chelsea had all the finesse required to win. Birmingham, sixth in the Championship, are trying to muster the momentum that could take them back to the top flight but their main feat here, with a greatly weakened line-up, was to match Chelsea before the interval. Even then they were tame. Despite the mundane quality of the win, this was still quite a night for Di Matteo.

As a former Chelsea player he could draw on the sort of instinctive affection that was unavailable to Villas-Boas. Even so, the visiting fans seemed more intent on vetoing candidates than endorsing the caretaker manager. They were blunt in a chant that scorned the very notion of Rafael Benítez filling the vacancy.

The man in charge of Chelsea here does not depend solely on the affection of fans. Di Matteo may have been dismissed by West Bromwich Albion but there had been fine play and some good results before he suffered the rapid fall from grace.

This win would have been welcomed. Chelsea have taken full points from just five away matches so far in this Premier League campaign. The challenge here was of a lower order but Chelsea still had to be efficient.

Lampard, a box-to-box midfielder who turns 34 in June, was perhaps on the bench because Di Matteo sensed that he would do better by coming on as Birmingham faded. Even so, the match was mundane throughout. In general, there was a lack of individuals capable of menace.

A header by Birmingham's Nikola Zigic that was tipped over the bar by Petr Cech in the 39th minute had to be deemed a highlight. When Fernando Torres did turn his marker and make space at the close of the first half, his effort was skewed off-target. This cannot have been the sort of quiet sought by Chelsea after the tumult of Villas-Boas's departure. Whoever does fill the vacancy will realise how much of a task he faces.

The torpor in this game was stubborn in its refusal to leave the premises and the second half maintained the emphasis on industry over imagination. There was at least a hint of incisiveness in the 51st minute as Salomon Kalou played a pass to Mata inside the penalty area that called for a smart tackle by Pablo Ibáñez. There was at least an indication then that Birmingham might buckle. The player who had been denied was soon to prevail.

After 54 minutes Ramires crossed from the right and a blocked attempt by Salomon Kalou rebounded to Mata, who took his goal with a low finish. With an hour gone Raul Meireles extended the lead by shooting high into the net from the edge of the area.

There might have been a third nine minutes later but Mata's penalty was saved by Colin Doyle after Guirane N'Daw had brought down Torres. All the same, there was little angst for anyone in Chelsea's colours.