LONDON—You have to feel for Marin Cilic. He’s the defending champion at the Queen’s Club tournament, but he’s yet to play on Centre Court. It feels like people have forgotten his win here, although they certainly remember David Nalbandian’s infamous default for unsportsmanlike conduct in the final last year.

Now Nalbandian is nursing a rib injury and a brand-new daughter, and Cilic is one of three former champions left in the draw (there's Andy Murray, while the third, Lleyton Hewitt, knocked out a fourth, Sam Querrey, in three sets earlier). While Murray, Juan Martin del Potro and Jo-Wilfried Tsonga all take to Centre, Cilic has to struggle through three frustrating sets on Court 1 to earn his quarter-final spot.

I find it surprising that Cilic’s opponent, Feliciano Lopez, only has a solitary semifinal appearance in seven attempts at this tournament. I find it less surprising after I watch him lose a match he really should have won, in which he barely stopped talking from the first ball to the last. He’s furious with the umpire about two early overrules—‘Do you want me to lose this match?’ he demands repeatedly of Magdi Somat in the chair—and he’s not keeping his displeasure to himself. He starts echoing the ‘out’ calls at the top of his lungs and sarcastically congratulating the umpire on not overruling.

All of this coming makes Cilic appear more saturnine than ever. He’s timing the ball badly on his forehand side, a perennial problem, and he’s not getting down low to Lopez’s slice with his more reliable backhand. There doesn’t seem to be the same extreme back bend that used to characterize his serve, nor such a snap on it, either. Two forehand misses give up the crucial break to lose the first set 6-4, and he’s broken at the start of the second as Lopez, still chirping away, yanks him all over the court, bringing him in only to crouch low and unfurl beautiful backhand passes down the line.

Lopez has to serve to consolidate as first Murray’s post-match interview and an extended introduction to the next match blares over the P.A. from Centre; not ideal conditions for a man who’s been annoyed and rattled by just about everything today. He floats a couple of slices out, then double-faults after Cilic unleashes a storming forehand down the line. In a tiebreak which consists mainly of aces, it’s Lopez who cracks first, framing a forehand long, and Cilic aces to take the second set.

It’s against the run of play and Cilic is promptly broken when he dumps a backhand in the net, but at 2-5 and match-point down, he charges into the net and Lopez can’t make the pass. Finally Cilic seems to loosen up, standing straight and stepping into his backhand to dominate the next point from the baseline, giving himself staccato bursts of encouragement between points. Cilic produces his best tennis so far, testing his charging opponent with low passes, and Lopez can’t serve out the match.

It still doesn’t feel like the match is in Cilic’s hands at all. He redirects the ball neatly off a dropshot to bamboozle Lopez at net, but on break point—with a chance to serve for the match on the line—he frames yet another forehand. Lopez hovers by the baseline, watching the ball, waiting for an out call that doesn’t come; as it drops—and still no call. He pats the ball back into the court and howls. He finds it impossible to believe that the umpire hasn’t overruled; I find it impossible to believe that, given his earlier well-publicized feelings about the umpire and the line-calling, he hasn’t been more careful. But either way, despite another long rant from Lopez—‘You were waiting for this moment! Everybody saw the ball out!’—Cilic serves it out for the win.

It’s a frustrating match, in the same sense that Cilic’s career is slightly frustrating to watch; you’re constantly on the edge of your seat, waiting for this talented young man to impose himself. Watching Cilic return to Court 1 later to play doubles with del Potro, I’m reminded of a moment—I’m sure there was a moment—years ago when these two, born five days apart in 1988, were spoken of as the potential next generation to dominate tennis. It never quite happened.

Side by side, both 6’6”—at least according to the ATP website; del Potro is clearly taller—it’s easy to understand why people got so excited about these two when they burst on to the scene. They’re different, of course: del Potro is more heavily-built and physically imposing, while Cilic is a genuine beanpole; Cilic is more prone to the rueful smile, del Potro to the doleful sigh. Everything del Potro does is a little calmer, a little cleaner, a little more deliberate; Cilic is a little quicker, a little whippier, a little more energized. Del Potro is less reluctant to approach the net, a little more solid at it.

But they’re recognizably the same breed of player—a breed which, moreover, used to be spoken of excitedly as a new breed: The big men who could move surprisingly well and back up big serves with power and consistency off the ground. They even ran into each other on the way to their respective career-best achievements—del Potro beat Cilic in the quarterfinals of the 2009 US Open, and the Croat returned the favor in five on his way to the 2010 Australian Open semifinals. Neither has had such a good major tournament since. There have been injuries, there have been strings of first-round losses, there have been agonizingly close five-set losses. Del Potro is firmly ensconced inside the Top 10, Cilic just outside it. They’re up there, they’re just not right up there.

Tonight, they’re playing the kind of tennis that doubles purists hate; mainly standing back and pounding forehands at Daniel Nestor and Robert Lindstedt, who are having a torrid time of it (Nestor and Lindstedt eventually lose in the super-tiebreaker after a strong second set). It can’t be a great feeling to have these two show up and lazily pummel your serves and groundstrokes at the end of a long day, and the veterans look grim.

In contrast, Cilic and del Potro look young tonight; something about the two of them muttering and grinning together makes them look like kids, overgrown boys taking some kind of make-believe game far too seriously. It’s getting darker and colder. But they’re having fun.