No 7 seed Tommy Paul advanced to the last eight of the Mexican Open when Michael Mmoh retired on Wednesday at the Princess Mundo Imperial in Acapulco.
Paul, ranked No 23, was leading 6-4, 2-2 when Mmoh, ranked No 86, pulled out of the second round match due to injury.
Tommy Paul will face fellow American Mackenzie McDonald next. He had defeated Ecuadorian Emilio Gomez (6-1, 7-6 (4)) in the previous round of the Acapulco Open.
In the first round. Michael Mmoh had scored a win over Marcos Giron (7-6 (3), 6-1).
Acapulco ATP500, other second-round matches (Princess Mundo Imperial, hard, USD 2.013.940, most recent results first):
- Frances Tiafoe (6) beat Feliciano López (WC): 6-2, 7-6 (6)
- Mackenzie McDonald beat Brandon Nakashima: 6-2, 6-0
- Nuno Borges vs. Holger Rune
- Elias Ymer vs. Matteo Berrettini
- Taylor Fritz vs. Denis Shapovalov
- Alex De Minaur vs. Jacopo Berrettini
- Taro Daniel vs. Casper Ruud