Novak Djokovic moved into a 10th consecutive US Open semi-final but benefited from yet another retirement against Jo-Wilfried Tsonga.

The world number one held a 6-3 6-2 lead over Tsonga when the French ninth seed retired due to a knee injury on Tuesday.

It has been the story of Djokovic's tournament in New York, having had a walkover in the second round and retirement in the third.

Despite his lack of competitive action, the Serbian defending champion still appears in fine form, and faces another Frenchman in Gael Monfils in the last four.

Djokovic has reached at least the semi-finals at every US Open since his runner-up finish in 2007, now just two shy of Jimmy Connors' record.

Tsonga had his chances in the first set but was predictably punished by Djokovic, who was consistent as his opponent faltered.

The errors from Tsonga continued in the second set before he needed treatment on his knee.

He decided to call it quits at the end of the set, suffering defeat to Djokovic for the 16th time in 22 matches.

Monfils has an even worse record against Djokovic, sitting at 0-12 win-loss heading into their semi-final.

STATISTICAL BREAKDOWN
Djokovic [1] bt Tsonga [9] 6-3 6-2 ret.

WINNERS/UNFORCED ERRORS 
Djokovic – 18/12
Tsonga – 11/36

ACES 
Djokovic – 1
Tsonga – 3

BREAK POINTS WON  
Djokovic – 4/9
Tsonga – 1/2

FIRST SERVE PERCENTAGE  
Djokovic – 58
Tsonga – 57

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE 
Djokovic – 83/57
Tsonga – 70/28

TOTAL POINTS  
Djokovic – 64
Tsonga – 44