They created a series of chances before John Sutton rounded Jamie MacDonald and found the net from a tight angle.
The victory secured Motherwell's sixth consecutive top-flight victory - the first time they have achieved that in 77 years.
McCall said: "It wasn't something that was on the forefront of my mind.
"That's five wins away on the bounce. We had an opportunity to do that here a few years ago on Christmas Eve and Hearts beat us 2-0, so I was more aware of that stat. It's all down to the lads in the dressing room, they have bounced back terrifically well."
McCall added: "First and foremost, I thought Hearts' second-half performance shows the spirit is still here. The kids were terrific.
"I'm not saying we should have made it easier for ourselves because MacDonald made two fantastic saves. I was really pleased with the way we played first half."
- Sports & Recreation
- Jamie MacDonald