WATCH: Del Potro directs frustration at Paris spectator

The best player can lose his cool on occasion, even if he's known as the "gentle giant." Juan Martin del Potro took his frustration out on a fan during his quarterfinal Roland Garros encounter with Marin Cilic—though he couldn't quite figure out which spectator to zone in on.

Someone in the stands cried out during his serve, disrupting his focus as he double faulted and handed Cilic a critical break for 5-4 in the second set.

"It was someone who made a loud [sound] before my serve, and I made [a] double fault," Del Potro said. "That's why I got angry with someone. I couldn't find the right person. But I get closer to them, just asking who was it? But I'm still trying to find the right person.

"But anyways, then it was my fault. I mean, the crowd are amazing, and that happens very often. But I wasn't focused in that moment, so I made the mistake."

Take special note of the ball girl, unfazed as she dutifully holds his towel during the exchange.

Del Potro would recover to win the match, 7-6 (5), 5-7, 6-3, 7-5. He needed two days to get it done after rain suspended play on Thursday when they were locked in the first-set tiebreaker. It marks the world No. 6's first French Open semifinal since 2009.

The 29-year-old was in tears after the win. He's come a long, long way.

"Everybody knows that I was close to quit this sport two years ago, but then I, for one reason, I never give up. And I have been trying and trying every day to fix my problem in my wrist," Del Potro said. "And in the end, I got it, and now I'm having a great present, looking forward for the future."

For his hard work, Del Potro gets a semifinal showdown with Rafael Nadal on Friday. The last time Del Potro contended a Grand Slam final, he won it at the 2009 US Open.

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