Second-bottom Well travel to face local rivals Hamilton Accies on Saturday with only three games left.
The Lanarkshire duo are level on points, with both four clear of bottom-placed Inverness Caledonian Thistle.
"It's a big game at the best of times, but given the situation we are in, it is obviously magnified even more," Lasley said.
"Has everything been perfect this season? Of course it's not. Have there been mistakes? Of course there have, we have all made them. Every single player in the squad has made mistakes.
"This is not the time for saying 'you did this, you did that'.
"It's togetherness, especially going into a derby game. That's what the fans expect of us and we expect of ourselves, to go in there together and we need to show that on Saturday."
Both Lanarkshire sides have lost their two games since the Scottish Premiership split into two, leaving them in a perilous position.
A victory on Saturday could keep them safe from automatic relegation if Inverness lose and Lasley admits the game is as important as any in his 16 years at Fir Park.
"This is a one-off game, it almost becomes a play-off," the 37-year-old said.
"We are capable of winning that game on Saturday, there is absolutely no doubt about that.
"What we need to be is the best version of ourselves to give us a good chance.
"We have had second-placed finishes, Europe, that's gone. It was great, it was absolutely fantastic.
"This is the here and now and we have got to win a game of football on Saturday. It's as simple as that.
"The best way to do that is for us and the fans and for everyone to be together.
"Hopefully, that's the case on Saturday and I'm sure it will be.
"I'm sure we will have a fantastic support there again. It's up to us to do the business on the park to reward that."
Motherwell captain Keith Lasley has urged his team-mates to pull together as the Fir Park side fights relegation.