Brentford manager Mark Warburton was annoyed to see his side let a two-goal lead slip late on in their 2-2 draw at Milton Keynes Dons despite achieving their main goal of promotion on Friday.
Izale McLeod's header in the third minute of added time ended a run of five straight home defeats for the Dons while also securing the Sky Bet League One title for Wolves, who won at Leyton Orient earlier in the day.
Warburton said: "The players are frustrated because we were 2-0 up with 15 minutes to go and controlling the play.
"We've got to learn from that - we gave the ball away in poor areas.
"This is a difficult time of the year because we've achieved our main goal, but the players know that we must do better in the final 15 minutes.
"We've watched their penalty back and it's 50-50 so it's a tough one for the referee to call, although we feel he (goalkeeper David Button) gets the ball then the man but it was a tough call.
"We want to be professional in our remaining games and the players want to win for the fans because we had three and a half thousand fans here.
"They pay their money and we've got to put on a show and be professional in what we do so there's motivation required for the players."
Brentford looked certain to be heading for another victory when James Tarkowski's opener on the stroke of half-time was added to by Clayton Donaldson's neat finish.
But the Dons ended a home goal drought of over 10 hours when Stephen Gleeson scored from the penalty spot after Bees goalkeeper Button had fouled McLeod.
And McLeod had the last word at the death as he sent a superb header from Ryan Hall's cross into the top corner.
MK Dons boss Karl Robinson said: "I thought that their hunger, desire and work ethic was there for all to see and I've questioned that in recent weeks.
"I really think they put up a fight and I've said to Izale that when you work hard and fight for the cause then you get your little bit of luck.
"He's won a penalty and he's scored an equaliser for us in the last minute so it was nice.
"It was a tremendous relief and a weight lifted off a lot of people's shoulders with the burden of not scoring at home although we didn't feel as if it's had a massive effect on us.
"This was all about the work ethic - we worked extremely hard and we didn't deserve to go in at half-time 1-0 down.
"I thought we stood up to the test really well in the second half against a team celebrating promotion."