Novak Djokovic suffered a shock defeat to the Czech Republic's Jiri Vesely - ranked 123rd in the world - in the quarter-finals of the Dubai Tennis Championships, which will see his stint as world number one come to an end.

The 20-time Grand Slam winner eased past Lorenzo Musetti and Karen Khachanov into the last eight and was expected to stroll through to the semi-finals on Thursday.

However, qualifier Vesely marched to a 6-4 7-6 [7-4] win over Djokovic, with the vital break coming in the sixth game of the first set after a double fault from the Serbian.

Vesely broke Djokovic's serve one more at 3-3 in the second set and was serving for the match at 5-4, but the number one seed held his nerve to break back and ensure at least another two games.

The showdown would ultimately be decided via a tense tie-break, where Vesely hit a terrific forehand winner before collapsing in awe at his second successive win over Djokovic.

"It's an amazing feeling, I never thought I would have a chance against Novak," an emotional Vesley said during his on-court interview. "He's one of the greatest of all time if not the best.

"It's unbelievable, I have so many emotions it's hard to describe. He's such a great ground-stroker and moves unbelievably well, you have to fight for every single ball. I think I did an amazing job today."

Vesely could now meet fellow qualifier Ricardas Berankis in the semi-finals should the Lithuanian overcome Denis Shapovalov in their quarter-finals, and Djokovic's exit means that Daniil Medvedev will now become the new world number one.