Saturday's enterprising first-half display by Motherwell was finally rewarded in the final four minutes when Steven Saunders scrambled home his first career goal and John Sutton headed home his 12th of the season.
Hearts had won four of their previous five home games to revive their hopes of finishing in the European places in the Scottish Premier League.
But they failed to mount a comeback after the break and Motherwell could have added to their lead as they moved into fourth spot, seven points ahead of Hearts with a goal difference superior by 13.
Jefferies said: "We can't have any complaints. The two goals are set-plays again but I think overall Motherwell were worthy of being a couple of goals up.
"They were better than us at passing, they were better at holding the ball, they worked harder than us. They didn't make it as easy for us as we made it for them.
"They had two strikers who were prepared to battle for everything and give our defenders a torrid time. We didn't do that at the other end.
"In the middle of the park we were too far off them, when we lost possession they were breaking and we were nowhere to be seen.
"The second half we were better and got tighter but I told them the least we expect is a desire to win.
"We looked like a team that maybe settled for getting in the top six and that's not acceptable.
"It's not all over, they have to go and concentrate on trying to win the next three games, but they won't with application like that."
Motherwell manager Craig Brown felt he had been vindicated after continuing to praise his team's general performances in the wake of four consecutive defeats.
Brown revealed he had been encouraged by the passion shown by his players, even when midfield team-mates Steve Jennings and Giles Coke squared up to each other in the first half.
"I was delighted," he said. "It's great when they are so passionate. It wasn't an incident that was going to cause any disharmony.
"They are two very passionate players. I want the team to be passionate and I want them to be fighting.
"It was a mild disagreement, you've seen worse than that. At half-time it was calm, they are good friends.
"I'd have been fining them if they had been doing that to an opponent but, internally, healthy determination to succeed is what I would describe it as."