(Photo credit: Albert Cesare/The Enquirer / USA TODAY NETWORK via Imagn Images)

Reilly Opelka smacked 14 aces and saved all seven break points while posting a 7-6 (6), 6-4 upset victory over No. 6 seed Alex de Minaur on Sunday to reach the third round of the Cincinnati Open at Mason, Ohio.

Opelka defeated de Minaur for the first time in six all-time meetings. He had 35 winners and converted 75.6 percent of his first-serve points.

'My forehand helped me a lot and my backhand, playing with a lot of offense and I was pretty consistent from the baseline the whole match,' Opelka said. 'My serve fluctuated, and it was a bit of a surprise that the other things came through well for me today. I think I returned really well too.'

Another factor was that de Minaur had just six winners and two aces. The Australian standout's failure to convert a break point was also a key element in the match.

Opelka will next face Argentina's Francisco Comesana, who advanced by beating 29th-seeded Luciano Darderi. Comesana led 6-4, 3-1 when Darderi retired due to a lower-back injury.

Second-seeded Carlos Alcaraz wasn't overly sharp, but the Spaniard notched a 6-1, 2-6, 6-3 victory over Bosnian Damir Dzumhur.

Alcaraz had 44 unforced errors and just 21 winners. He also failed to save any of his three break points.

'It was just a rollercoaster,' Alcaraz said. 'Lots of good feelings, bad feelings, back to the good ones. All I can say is I am happy to get the win at the end and just have another chance to be better.'

'I will try tomorrow to have my confidence back because today it was a little bit tricky,' he continued. 'Damir plays really smart tennis, which I have to be focused and ready for that.'

Dzumhur had just 11 winners and made 36 unforced errors.

In other matches, No. 9 Andrey Rublev of Russia defeated Learner Tim 7-6 (4), 6-3, and Australia's Adam Walton recorded a 6-7 (0), 6-4, 6-1 win over No. 12 Daniel Medvedev of Russia. No. 16 Jakub Mensik of the Czech Republic notched a 6-4, 6-2 triumph over Ethan Quinn.

No. 21 Alexei Popyrin of Australia knocked off Spain's Martin Landaluce 7-6 (3), 6-3, while Czech Jiri Lehecka, the No. 22 seed, rallied for a 4-6, 6-1, 6-4 win over Tristan Boyer.

Spain's Roberto Bautista Agut registered a 6-4, 6-3 victory over No. 32 seed Cameron Norrie of Great Britain. Jenson Brooksby beat France's Arthur Cazaux 7-5, 6-1.

--Field Level Media