What a difference a week can make. Until they arrived in Montreal, Juan Martin del Potro and Milos Raonic were heading in opposite directions. Del Potro, semifinalist at Wimbledon and champion in Washington, D.C., was fast becoming everyone’s favorite dark horse pick for the U.S. Open. At the same time, Raonic had been floundering his way through a lost summer. But when they met in the round of 16 on Thursday, the trajectories were reversed, at least for a day. It was Raonic who gave his season a bounce with 7-5, 6-4 win.

Granted, this match came with all sorts of extenuating circumstances, both physical and moral. Del Potro, who was stretched to 7-5 in the third in his previous match by Ivan Dodig, was suffering from back pain. He struggled to generate pace on his serve and watched as a few gettable balls sailed past him. Raonic had his own physical issue, a “numb” feeling in his serving arm. After the third game of the match, he was given an overly long, 12-minute medical timeout to work on it. The break took the life out of del Potro, the crowd, and the match, as both players fought their bodies as much as their opponents through two dull sets of big-man tennis.

Almost two sets of dull, big-man tennis, I should say. The final, and most memorable, extenuating circumstance of the match happened with del Potro serving up a break at 4-3 in the second. Raonic ran forward to put away a short ball and hit what looked like a winning inside-out forehand. But before the ball could bounce twice, his foot slid forward and touched the bottom of the net. Raonic gave chair umpire Mohamed Lahyani a guilty look, but no call came, from either player or umpire. Lahyani either hadn’t seen the touch or had judged that the ball was already out of play—when the point was replayed on the stadium Jumbotron, Lahyani admitted that he had made a mistake.

That, at least was an honest mistake. How about Raonic’s? Should he have called the point against himself? There’s no question that a player should tell the umpire if he touches the net in a middle of a point. But when he hits a point-ending shot, is it also his job to decide whether that shot was still in play when he touched the net, and that he should forfeit the point? In general, I think that’s too much to ask of a player; those kinds of judgments are why we have umpires. In this case, though, while the person most at fault was Lahyani, it seemed to me that Raonic knew he had touched the net while the ball was in play, and he should have given the point to del Potro.

The upshot was that del Potro, who didn’t seem especially eager to have to play any more matches with a bad back, didn’t win another point. It’s too bad that Raonic’s performance will be remembered for his no-call, because he played some good tennis for a man with a numb arm. Raonic hit 39 winners to del Potro’s 10, and was 14 of 17 at the net. His new coach, Ivan Ljubicic, has been urging him to use his forehand more and play with more dynamic aggression. Thursday was the first time that we saw it work for him.

Del Potro will try to heal his back before Cincinnati, and regain his summer mojo there. Raonic, with some mojo—good and bad—of his own for the first time in months, moves on to face fellow upset artist Ernests Gulbis.