A John Terry red card used to be a major headache for Chelsea, but on this occasion it may well have helped make up the minds of those responsible for deciding whether or not the defender plays on for the club past the end of this season.
With Chelsea top of the Premier League without Terry in the team or even on the substitutes' bench, it already looked most unlikely that the 36-year-old would be offered an extension to his contract that expires this summer.
This time last year, Terry publicly revealed that there had been no talks over a new deal and suggested that last season was likely to be his final hurrah with the club.
The interview ensured that Terry's name was sung by the Chelsea faithful at every remaining game and the club eventually relented and handed their "captain, leader, legend" a new deal.
But if Terry's intention was to use his first start since October to show Chelsea that he should be kept on once again, then it went horribly wrong.
The day had already started badly for Terry and his Chelsea prospects, as the club confirmed that left-footed defender Nathan Ake had been recalled from his loan at Bournemouth.
And it got much worse in the 67th minute, when Terry capped what had been a rusty performance against League One opposition by getting his marching orders.
Kurt Zouma, returning from almost a year out, failed to cut out a low pass from Peterborough captain Chris Forrester, which sent Lee Angol scampering towards goal. Unable to catch the visiting striker, Terry produced what could only be described as a rugby tackle to bring him down.
Terry appeared to be laughing as he was called over by Kevin Friend, but the referee did not see the funny side as he produced a red card.
Fortunately for Terry and Chelsea, the tie was effectively over by that point and Antonio Conte's team progressed to the fourth round thanks to a brace from Pedro and goals from Willian and Michy Batshuayi.
Asked about Terry's red card, the head coach, Conte, said: "It wasn't right, this decision. He didn't take the opponent and, behind John, there was Ivanovic, to cover him.
"It's a pity because to take a red card is not good. You have to respect the ref's decision, but, in this case, maybe we will do an appeal."
On Terry's future, Conte added: "We are in January. It's important to make this decision together with the club and not alone. I am pleased for John because he is showing me great commitment, when I ask him to play, when he doesn't play, because he is helping me a lot. It's important to continue in this way."
Conte, though, confirmed Terry faced greater competition to win back a regular place in Chelsea's three-man defence from the recalled Ake. "I recall Ake because I think he is showing he is ready to stay in the squad," said Conte.
"He gives me an important option because we are playing with three central defenders. He can play on the left or in the middle and we must see in training if he can play at wing-back."
After it emerged Chelsea are considering a surprise bid for Swansea City striker Fernando Llorente, Conte had stated that Batshuayi, who is wanted on loan by West Ham United, Crystal Palace, Swansea, Lille and Sevilla, needed to make the most of his fourth start since his £33 million move from Marseille.
Those words appeared to weigh heavily on the 23-year-old for much of the first half as he looked to be trying too hard to score.
But two minutes before half-time, Batshuayi got the goal he craved. Willian played a good pass out to Branislav Ivanovic, whose cross was cushioned by Ruben Loftus-Cheek for the Belgian to pick his spot.
Batshuayi's goal doubled Chelsea's lead, as Pedro, standing in at left wing-back, had opened the scoring in the 18th minute with a super strike after cutting back on to his right foot.
Despite the fact the Premier League leaders went in at the break with a two-goal cushion, League One Peterborough had caused the Chelsea defence some problems.
Marcus Maddison picked out Angol unmarked in the Chelsea penalty area in the eighth minute, but his volley was straight at Asmir Begovic. Ryan Tafazolli headed wide from a Maddison corner.
Conte appeared to use the half-time break for a quick trip to the Chelsea megastore as he remerged for the second period wearing a white club-branded waterproof jacket and a blue baseball cap.
While members of the press box debated his choice of clothing, Loftus-Cheek should have added a third goal when Batshuayi set up the England Under-21 midfielder, who rolled the ball wide.
It took only until the 52nd minute for Chelsea to kill the tie, however, as Willian received the ball from Pedro and cut in from the left to send a shot low into the net.
Terry's dismissal forced Conte into a reshuffle and, as 10-man Chelsea were adjusting, Tim Nichols pulled a goal back in front of the 6,000 visiting Peterborough fans.
Any dreams of what would have been one of the great FA Cup fightbacks were crushed four minutes later as Pedro scored again.
Peterborough manager Grant McCann said: "For 15 minutes, I thought we were very good. The difference in the game was they were clinical, we weren't. It was a good learning curve for our boys. I don't think we came here and disgraced ourselves."