Aberdeen were without a string of central midfielders, with Lewis Ferguson suspended, Funso Ojo still out injured and both Stephen Gleeson and Craig Bryson on the bench but not fully fit following injury.

And McInnes got more than he could have hoped for out of his unfamiliar pairing in the middle of a 4-2-3-1 formation.

"We have worked all week with Leigh and Vyner in there," he said. "I naturally feel Zak can play that role, I think that's where he is going to end up playing his best football in his career. But Greg really took to it.

"I thought the two of them were instrumental in our performance. Obviously Greg gets an assist and Zak gets a goal, but I thought their performance was fantastic. And it gave us a good platform."

Joe Lewis also gave the Dons the opportunity to go on and win by saving James Scott's fifth-minute penalty after being adjudged to have felled Christopher Long.

Cosgrove chipped Mark Gillespie 10 minutes later after Leigh had dispossessed Long and sent the striker past Barry Maguire, who was briefly standing in for Peter Hartley as the Motherwell centre-back received treatment.

Niall McGinn took the ball off Allan Campbell before netting the second and Vyner completed the scoring on the hour mark.

"We had to do it the difficult way," McInnes said. "It's not a penalty. I have watched it back and I don't see a touch. Joe is adamant there is no touch.

"And thankfully Joe has made a brilliant save. And when you've got your keeper doing that after five minutes and Sam finishing with that confidence, that inspires the rest of the team. Your goalie and your number nine doing that sends out the confidence.

"From going ahead, I thought we were very good in the game."

Motherwell manager Stephen Robinson felt the match gradually slipped away from his side.

"I thought the key moments in the game went against us," he said. "We started really well, dominated the whole first half. We miss a penalty at a crucial time, it gives them a little bit of a lift.

"Then Peter goes off, we are down to 10 men, we are trying to assess him to make sure he's OK or not and Barry goes in at centre-half and makes a poor decision and we get done.

"Then Allan gets caught on the ball for the second goal and we get punished by a great finish."

Robinson somewhat reluctantly took Hartley off immediately after the goal and handed Bevis Mugabi a debut.

"He seemed fine to me," Robinson said. "He seems fine now but we can't take any risks nowadays. The doctor wasn't comfortable with him going back on again and we have to err on the side of caution always."