John Sutton, Iain Vigurs, Lionel Ainsworth and James McFadden were all on target for the second-placed Steelmen, who stay 11 points behind Celtic after a fifth straight win in the Scottish Premiership.
McCall was delighted with Motherwell's free-flowing football and heaped praise on his players.
"I thought it was a fantastic performance," he said. "We keep reverting back to last season and the season before and the players we have lost, but I thought the second half was as good as we have been, on a par with anything.
"The football was terrific and we have created some fantastic chances. Bear in mind it was against a side who don't lose a lot of goals.
"It was a good game. St Johnstone could have scored a couple, they have hit the woodwork a couple of times and we hit it three or four times.
"We said it might not be a day for pretty passing but they passed it well and moved. I was really proud of the performance. I thought it was the perfect all-round way to start the new year. It was just a delight."
Ainsworth netted his fourth goal in as many games and McCall expects him to extend his loan spell from Rotherham, which ends after next Saturday's match against Inverness.
"I think we are going to have to pay him a little bit more than we were paying which is unfortunate and we probably haven't got it, but he has scored four in four so the money keeps going up," said McCall.
"But we are hopeful. There was dialogue on Tuesday and hopefully it will be sorted in the next couple of days."
Tommy Wright was unhappy with Saints' sluggish start and believes his side paid a heavy price for slack defending.
"It's a strange game at times because it could have been 4-3 at half-time," he said.
"We didn't start the game well, which was key. We let them get a good foothold in the game and the tempo they played at.
"We settled down and created enough chances in the first half to be level but we did contribute to our own downfall.
"The goals are poor from our point of view, ill-discipline and not dealing with one against ones, giving away soft free-kicks to a team that has good delivery.
"It could have been 6-4 to them because there were a lot of chances."