The German ran out of steam today but he's pleased with how far he came and what might come next.

Alexander Zverev is bitterly disappointed that he couldn’t do more in his first Grand Slam quarterfinal on Tuesday in Paris. But the 21-year-old German is also buoyed by the belief that he is now ready to step up on the game’s biggest stages. Zverev won three straight five-setters in Paris and reached his first career quarterfinal at a major, answering a lot of questions about his ability to back up his exceptional results at the Masters 1000 events.

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Unfortunately on Tuesday Zverev paid the price of doing all that hard work in his last three matches and came up lame in the first set against Dominic Thiem. He suffered throughout the straight-sets defeat but was not at 100 percent and thus susceptible to the grinding game of Thiem over the course of the Austrian’s 6-4, 6-2, 6-1 win.

Did he think about pulling the plug after injuring his left hamstring early in the first set?

“I definitely thought about it,” Zverev told reporters, “but I didn’t want to pull out for the first time in my career in a Grand Slam quarterfinal.”

He added: “I knew I’m not going to win the match. There was no way for me. I could barely move. I couldn’t serve, I couldn’t really do anything. But I still wanted to finish the match and give the credit to Dominic—he deserves to be in the semifinals and [I wanted the match to] end on a loss and not on a retirement.”

Tennis Express

Despite the loss, Zverev has taken a major step in his development, and he clearly took much solace from his three marathon wins earlier in the tournament.

"It showed I'm physically one of the strongest players," he said. "I can last very long. I can last five-set matches in a row, how I showed. Unfortunately an injury held me back.”

The next step is very much within reach, says Zverev, who at just 21 has only played 12 Grand Slams in his young career.

"This is a very positive week for me,” he said. “My first quarter. I lost to a great player. I was hurt a little bit. So who knows? Who knows what could have happened?"