DUBAI: Novak Djokovic lost his Dubai quarter-final and his world number one ranking in one go on Thursday as he suffered a 6-4, 7-6 (7/4) upset at the hands of Czech world number 123 Jiri Vesely.

Competing in his first tournament of the season, and first since getting deported from Australia, Djokovic needed to at least reach the semi-finals in the Emirates to try and stop Daniil Medvedev from replacing him at the top of the rankings.

But Vesely had other ideas as the left-handed qualifier improved his career record against Djokovic to 2-0 - a result that will see Medvedev become the first man since 2004 outside the "Big Four" - Djokovic, Rafael Nadal, Roger Federer and Andy Murray - to occupy the number one ranking on Monday.

Djokovic, who has spent a record 361 weeks as the world number one, said at the start of the tournament that he "would be the first to congratulate" Medvedev, if the Russian succeeded in his quest for the summit.

US Open champion Medvedev, currently involved in the Acapulco tournament, becomes the third Russian man after Yevgeny Kafelnikov and Marat Safin to ascend to the world number one spot.

Vesely, a former junior number one, has won five matches in Dubai so far this week, making it through qualifying to reach his first tour-level semi-final since Pune in 2020.

"It's an amazing feeling. I never thought I would really have a chance against Novak, he's one of the greatest of all time, if not the best," he said.

"After the last 12 months, I've been going through... it's unbelievable, I have so many emotions inside, it's hard to describe, it's just an amazing feeling," added Vesely, who next takes on Denis Shapovalov or Ricardas Berankis.

The 28-year-old came out victorious in his only previous meeting with Djokovic, defeating the Serb on the clay courts of Monte Carlo back in 2016.

Vesely started the match by breaking Djokovic on his way to a 2-0 lead.

He lost his advantage as the top seed struck back but some clever drop shots and some tricky lefty serves saw the towering Czech inch ahead once again and he served out the opening set on the 47-minute mark.

A down-the-line backhand drive earned Vesely a break in the seventh game of the second set but he wobbled while serving for the victory as Djokovic pegged him back to level for 5-5.

Vesely raced to a 3-0 lead in the tiebreak and soon completed a huge surprise win over the five-time Dubai champion.

   **- Sinner slumps -**

Earlier on Centre Court, second seed Andrey Rublev advanced to his third semi-final in as many weeks with a 2-6, 6-3, 6-1 victory over American Mackenzie McDonald.

Contesting a 12th consecutive quarter-final at the ATP 500 level, Rublev recovered from a poor first-set performance against McDonald to reach the Dubai semi-finals for a second year in a row.

The 24-year-old Russian will next face off with fifth seeded Hubert Hurkacz, who eased past Italian fourth seed Jannik Sinner 6-3, 6-3 in 84 minutes.

"Today I was thinking that for sure it's over, but somehow I was just trying to tell myself, 'Just keep fighting and we'll see what happens'," said an exhausted Rublev, who won both singles and doubles titles in Marseille last weekend.

"I lost twice to Hurkacz. It will be interesting for me. In the situation I am right now, completely tired, last times I lost against him, I have nothing to lose. I will try to go for it and we'll see what's going to happen."