Sometimes John Isner is one of the grittiest competitors in tennis. Other times he looks as if he’s lost all belief in himself and all love in the sport. Then there are matches, like his 7-6(4), 7-6(3) quarterfinal win over Ernests Gulbis on Friday, when the big American veers between those two states from one point to the next. Through much of the first set, Isner held serve with ease while looking semi-disinterested in the proceedings. At 2-3, Isner double-faulted twice to go down 15-30, but served his way clear for a hold; his second-serve kick ace at 15-30 bounced as high as I’ve ever seen a serve bounce. At 4-5, a mopey Isner went down 0-30 before suddenly springing to life with two aces and a forehand winner. Two games later, Isner couldn’t find his first serve and went down 30-40, set point for Gulbis. He'd been hitting his second serve tentatively during that game, but he went after this one and drew a return error. The same pattern held in the tiebreaker—at 2-3, a sluggish Isner woke up and cracked a backhand down the line, and served his way through from there. Most of the press room predicted a Gulbis explosion if he lost the first set; he’s smashed a racquet in all of his matches here so far. But Ernests held himself in check, and when he broke Isner at love to start the second, it looked as if his patience would pay off. But instead of riding the momentum shift, Gulbis’s own game began to fray—maybe he needed to release the anger, after all. Gulbis saved three break points at 2-1, and then twice let Isner stay in the set when the American appeared ready to pack it in and head to a third. At 1-3, Isner came back from 0-30 to hold, and at 2-4 he saved two break points that would have pretty much clinched the set for Gulbis. Just when it looked like Ernests would survive, he collapsed completely while serving at 5-4. He double-faulted for 0-30, hit a brain-cramp drop shot to make it 15-40, and missed the simplest of mid-court backhand putaways to hand back the break. Not only had he made the mistake of losing his serve with a chance to close out the set, he had let himself be drawn into another tiebreaker with Isner. When Gulbis double-faulted at 2-3 to give away the first mini-break, it was all but over. Gulbis, resigned rather than enraged, seemed to know it. It’s hard to think of many other players who have exploited the rules of tennis as thoroughly as 6’10” John Isner. Or at least two specific rules—the one that says players get two serves, and the one that says sets end in tiebreakers. It’s also hard to think of a player who has been so much better with a home crowd behind him. Maybe it’s his college team tennis background, but he likes to have the fans on his side, and he made a point of thanking his many supporters here today for helping him with this win, which put him back in the Top 10. Isner will need all of that help and then some tomorrow, when he faces Novak Djokovic in the semifinals.