At the Australian Open, Mackenzie McDonald of the U.S. put a scare into one of the ATP World Tour's best players in Grigor Dimitrov, pushing the Bulgarian to five sets. Fortunately for Germany's Alexander Zverev, there would be no such drama on Tuesday at the Abierto Mexicano Telcel presentado por HSBC in Acapulco.

The second seed dismissed McDonald 6-3, 7-5 in 81 minutes. His victory was in stark contrast to the two-hour, 23-minute struggle 2016 champion Dominic Thiem endured in his opening assignment as he eked out a 6-3, 5-7, 7-5 triumph over British qualifier Cameron Norrie.

Zverev, the World No. 5 in the ATP Rankings, was nearly flawless on serve as he won 75 per cent of his first-service points and erased the lone break point he faced. He will next meet fellow German Peter Gojowczyk, who reached the Delray Beach Open final on Sunday, a 6-3, 6-2 winner over Mexican wild card Lucas Gomez.

Two years ago in Acapulco, Thiem won the hard-court ATP World Tour 500 title. It remains his lone hard-court title to date.

On Tuesday, the World No. 6 improved to 8-1 at the Abierto Mexicano Telcel with his win over Norrie. The Austrian third seed let a match point slip as he was broken serving for it at 5-4 in the second set and Norrie broke again to even the match.

“Yeah very tough match. Should have been over earlier in the second set but didn’t close it out very well,” Thiem said. “It went over three sets and ended up a pretty big drama at the end, I would say.

“I was 5-4, 30-15 and then I made some easy forehand mistakes to lose a little bit of my confidence. It shouldn’t’ happen but yeah, what can I do now? The main thing is that I won and that’s all I care about.”

In the third set, the British World No. 113 in the ATP Rankings kept his nose narrowly in front on serve until the 11th game when Thiem broke for the chance to serve it out. The Austrian - a winner of nine ATP World Tour titles, including the Argentina Open in Buenos Aires earlier this month - delivered on his second match point to set a second-round clash with #NextGenATP Canadian Denis Shapovalov.

The 18-year-old scored an impressive victory over former World No. 4 Kei Nishikori 6-7(3), 6-3, 6-1 earlier on Tuesday. It will be his first FedEx ATP Head2Head encounter with Thiem.

“He’s a very, very good young player,” Thiem said of Shapovalov. “He’s one of the upcoming superstars of the game. So I’m looking forward to playing him for the first time.”

For the second time in three days, Argentina's Diego Schwartzman toppled Fernando Verdasco of Spain 6-2, 6-4. Schwartzman saved all five break points faced in the first-round contest. The 5'7” Argentine beat Verdasco in Sunday's Rio Open presented by Claro title match to win the ATP World Tour 500 crown, the biggest title of his career.

“It was a little bit easier because I have a lot of confidence after Rio de Janeiro,” Schwartzman said. “Today was not easy... I played good tennis. Felt well, and I need to recover well for the second round.”