MacLean made his first appearance in four months following knee surgery and stole the show with a first-half double, before Gary Miller added a third goal late on.
Wright, who saw his side bounce back from a 1-0 defeat at home to Inverness on Saturday, revealed MacLean had been desperate to come back into the fold but admitted he'd taken a bit of a gamble.
He said: "He's been badgering me for a few days now to put him back in.
"It wasn't a risk medically because his knee's fine, but perhaps a risk because he hasn't played.
"He could have had an U20 game but we didn't want it to be on plastic and most of them are on plastic (surfaces).
"You can see what he brings to us. He's a bubbly lad who gets about the pitch and makes things happen. I think he's a leader on the pitch and I thought it was a risk worth taking. He gave us a bit of a lift and some spark after Saturday.
"They (Motherwell) are one of the best teams in the country and I thought we dominated from start to finish."
Downbeat Motherwell manager Stuart McCall added: "Yet again we've come in at half time 2-0 down from two really poor goals.
"As much as St Johnstone were far better than us tonight in every department we can't give goals away.
"We lost too many individual battles. The pitch wasn't perfect to play football on but they (St Johnstone) moved it far better than we did.
"With a thin squad there's not a lot we can do at the moment - we probably could be doing with pulling a few people out at the minute and we'll have a look to try and do that."