Denis Olegovich Istomin (born 7 September 1986) is an Uzbekistani professional tennis player.

[7] Injuries resulting from a car crash in 2001 en route to an event kept Istomin away from tennis for 2 years, with doctors initially stating that he would never hold a racquet again.

[citation needed] Istomin first competed in the 2010 Aircel Chennai Open, but was defeated in the first round by Dudi Sela.

He made his first semi-final at an ATP level tournament at the 2010 SAP Open, in San Jose.

At the 2010 Pilot Pen Tennis Istomin advanced to his first ATP Final, but was defeated by Sergiy Stakhovsky in three sets.

At the 2010 Asian Games tennis finals, Istomin lost to India's Somdev Devvarman in straight sets.

[10] Istomin started the year at number 40 in the ATP rankings,[9] but had a poor run in the Australian swing, starting the year with a second round exit in Brisbane and then losing first round matches in the next two weeks in Sydney and then in the Australian Open.

In the following week, Istomin reached the second round of Key Biscayne (losing to then world number 2, and triple Grand Slam winner that year, Novak Djokovic), before making another three consecutive first round exits on the clay circuit (Monte Carlo, Barcelona, Munich).

Istomin's poor run continued on grass, with first round exits at Queen's and Eastbourne.

Istomin then beat Philipp Kohlschreiber in Wimbledon but lost to Mardy Fish, a top ten player then, in the second round.

Amidst the European summer, he then returned to clay and made a second-round exit in Gstaad in between first-round losses in Hamburg and Kitzbühel.

Following the US Open, Istomin returned to the Challenger circuit, where he won consecutive tournaments in Istanbul and Tashkent.

He finished the year at the 74th place of the rankings, still well inside the top-100[9] Istomin defeated both Florian Mayer and Tommy Haas en route to a quarter-final loss to Bernard Tomic, in Brisbane.

73 after the tournament, Istomin had to play the qualifying in Sydney, winning his three matches to qualify to the main draw, where he had an impressive run into the semi-finals as he swept past Pablo Andújar, Ryan Sweeting and 18-ranked Richard Gasquet, before losing to Jarkko Nieminen.

[9] In February 2012, Istomin advanced to SAP Open finals, losing to defending champion Milos Raonic of Canada.

At the Olympics, representing Uzbekistan, Istomin made the round of 16, losing to eventual silver medalist Roger Federer.

[12] During the USA hard court swing, Istomin made the second round of the Cincinnati Masters.

In January, Istomin advanced to the quarter-finals of the Brisbane International with wins over Martin Kližan and Lleyton Hewitt but was defeated by eventual champion Andy Murray.

Istomin reached the semi-finals of the U.S. National Indoor Tennis Championships where he beat John Isner, Lleyton Hewitt and Michael Russell before losing to eventual champion Feliciano López.

[citation needed] Istomin would start the new year in the 2014 Apia International Sydney Tournament.

He beat his first round opponent Pablo Andújar and then pulled off a huge upset to down 7th seed Croatian player Marin Čilić in straight sets.

[citation needed] He won all four points in the game consecutively with an ace down the middle, a running cross-court forehand passing shot, a backhand cross-court that was placed exactly on the line and an around-the-net backhand from behind the baseline, all of which were considered extremely risky shots.

Istomin won his first ATP world tour title at the Nottingham Open, where he defeated Sam Querrey in the final.

At the 2018 Asian Games, Istomin won the gold medal in the men's singles which would earn him a spot at the 2020 Summer Olympics.

[18] In February 2024, Istomin announced his retirement following Uzbekistan's 2024 Davis Cup match against Poland.