Marcos Andres Giron (/ɡiːˈroʊn/ ghee-ROHN; born July 24, 1993; Spanish: Girón)[2] is an American professional tennis player.

Giron won the singles title at the 2014 NCAA Division I Tennis Championships for UCLA.

[6] Giron reached the second round of a major for the first time at the US Open where he defeated Marc Polmans in five sets.

In November, Giron recorded his first top-ten win against seventh seed Matteo Berrettini at the Paris Masters.

[9] He participated in the main draw as a direct entry at the Australian Open for a second consecutive year.

[10] At the Open Sud de France, Giron was defeated in the first round by qualifier Tallon Griekspoor.

[13] At Halle, Giron reached his first quarterfinal at an ATP 500 level tournament as a qualifier where he was defeated by Félix Auger-Aliassime.

Giron made the second round at the Olympics, beating Norbert Gombos[15] before losing to Kei Nishikori in three sets.

[30] At the Monte-Carlo Masters, he was defeated in the first round by eventual finalist Alejandro Davidovich Fokina.

[34] On his debut at the Italian Open as a lucky loser, he upset 12th seed Diego Schwartzman in the second round.

He lost in the first round to German wildcard Jan-Lennard Struff, despite having two match points in the third set tiebreak.

[45] Getting past qualifying at the National Bank Open in Montreal, he lost in the first round to Roberto Bautista Agut.

[46] Making it past qualifying at the Western & Southern Open, he beat David Goffin in the first round.

[49] Seeded third at the San Diego Open, Giron reached his maiden ATP tour final after defeating Dan Evans in his semifinal match.

[69] He reached the third round at the 2023 French Open for a second time in his career and overall at a Major level defeating qualifier Hamad Međedović and Jiří Lehečka.

[71] At the ATP 500 2023 Japan Open Tennis Championships he reached the semifinals as a qualifier after defeating home favorite Yoshihito Nishioka, second seed Casper Ruud, his third top-10 win,[72] and eight seed Félix Auger-Aliassime, last two matches in straight sets.

[73][74] The following week at the 2024 Delray Beach Open, he reached for the first time a consecutive ATP semifinal (his sixth in his career), defeating Emilio Nava,[75] again fourth seed Adrian Mannarino this time in three sets, and wildcard Patrick Kypson.

At the beginning of the grass season, at the 2024 BOSS Open in Stuttgart, Giron defeated Andy Murray.

In Halle, he upset fourth seed Andrey Rublev, his first top 10 win on this surface, to reach the round of 16.

[77] His good form continued at the next grass court tournament, the 2024 Eastbourne International where he defeated defending champion and fifth seed Francisco Cerundolo in the first round.

[80][81] En route to the title, he registered wins over Alex Bolt in the quarterfinals[82] and Christopher Eubanks in the last four.

Giron reached the third round of the 2025 Australian Open for the first time defeating Tomas Martin Etcheverry in five sets.