Milton Keynes Dons manager Karl Robinson was left counting the cost of the 1-0 victory that ended Chesterfield's unbeaten Sky Bet League 1 start to the season.
Robinson saw his team take the points through a Benik Afobe strike early in the second half but he lost goalkeeper Dave Martin and right-back Lee Hodson with injuries.
Martin was replaced at half-time after he was caught late by Gary Roberts, who was booked along with MK Dons defender Kyle McFadzean in the melee that followed, and Hodson left the pitch on a stretcher minutes after Afobe pounced.
Chesterfield had the best of the first half but could not make their possession count and they missed a great chance at the start of the second when the ball ricocheted to Eoin Doyle but he curled wide from 12 yards.
It was an expensive miss because Afobe cut in from the right in the 49th minute and beat two defenders before driving a low shot inside Tommy Lee's near post.
Afobe should have scored again but missed badly from close range and Chesterfield almost snatched a point in stoppage time when Ian Evatt headed just over at the back post.
Robinson was pleased with the result but faces a worrying wait on the fitness of Martin and Hodson. "It wasn't so much the challenge on Dave, it was how he fell on his hip," he said.
"Lee Hodson landed on his ankle and he heard a pop but it's not swelled up as badly as we feared but it's possible ankle ligament damage and he will have an MRI scan."
But Robinson was delighted with the attitude of his players ahead of next week's Capital One Cup tie against Manchester United. "It's the biggest occasion in the lives of some of these players, they are playing one of the biggest clubs in the world and it's just around the corner," he added.
"But they care for this club and they understand that this is the nitty-gritty and what they get judged on and they've come here and played a really good side who have pushed us and that's probably the most difficult game we've played this season.
"But at times I thought we were very good and I think we've missed six good chances. Benik has scored the hardest one, and we have to put games to bed but it's a good win for us."
Chesterfield manager Paul Cook said: "Football is about winning and if you get beat you can't be happy. Managers always look for good performances but I always look for work ethic, desire and commitment and we had plenty of that.
"It s a tough league and there are some quality players as everyone has seen and it was a good game but unfortunately we've come out on the wrong side. The margins can be fine sometimes between winning and losing and I've never been one to get too high when you win and too down when you lose.
"It's a 46-game season and we will just go away and work hard. It's important that our lads have that important work ethic and when you are professional and put the work in, sometimes you get the rewards and the harder you work, the luckier you get."