Shenzhen Open top seed Alexander Zverev battled hard to stay in the tournament on Thursday. Zverev almost lost in his opener at the tournament to unseeded Steve Darcis. The 20-year-old narrowly beat the Belgian after a gruelling battle 4-6 7-6 (7-5) 7-6 (7-5). Darcis got off to a good start as he quickly broke Zverev. Darcis converted his third break of the match to open up a 2-1 lead. The world No. 76 then held on to his serve to close out the opener.

It didn't look good Zverev at the beginning of the second set either. Darcis broke the world No. 4 in the first game of the set. However, the 20-year-old managed to bounce back a couple of games later and make it 3-3.

Zverev was close to forcing a decider in the 10th game but didn't convert his set point on Darcis' serve. Darcis then broke Zverev to give himself a chance to serve for the match. Yet again, the No. 1 seed found a way to get himself back in the match as he broke the Belgian to clinch a tie-break.

Zverev seemed to be cruising to a decider once more as he had a 4-1 tie-break lead. But, Darcis refused to give up, winning the next three points to make it 4-4. The German then won two points in a row, sealing the set -- which lasted over an hour. The beginning of the third set was similar to the opening two sets. Darcis quickly broke Zverev to open up a 3-0 lead. The Belgian had a 4-1 lead before blowing two consecutive break points to go up 5-1.

Darcis paid the price for not converting his break point chances in the sixth game.

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Zverev battled to make it 4-4 in the third set. As no more breaks were seen, the set went into another tie-break. Darcis had a 5-2 tie-break lead and two services when he lost five points in a row and the match, eventually. It took over an hour for the third set to finish as well.

Almost three hours play

Zverev fired 15 aces and won 72 percent of his first serve points against Darcis. The No. 1 seed broke Darcis three times and saved 3-of-7 of the Belgian's break point chances. Interestingly, Darcis won a total of 113 points, while Zverev won 111 points during the match.

The clash came to an end after two hours and 48 minutes of play. Though not one of the best players in the game, Darcis has been a tough matchup for Zverev so far. The world No. 78 beat the world No. 4 in a Davis Cup match earlier this year. He was close to collecting his second win over the German but fell just short in the end.

Zverev plays Dzumhur next

Zverev is now set to meet rising Bosnian star Damir Dzumhur at the Shenzhen Open. Dzumhur handed a straight set defeat to qualifier Lukas Lacko 6-4 6-3. No. 6 seed Dzumhur and top-seeded Zverev have had no previous meetings. Zverev needs to improve his game as it won't be easy against the Bosnian. Dzumhur is coming off of a winning week at St. Petersburg. After claiming his maiden ATP title last week, Dzumhur won his first two Shenzhen matches in straight sets. He will be looking to continue his red-hot form and beat Zverev.