World number one Novak Djokovic has expressed his relief after advancing to the semi-finals of the US Open on Thursday.

The Serbian recovered from dropping his first set of the tournament to see off Mikhail Youzhny 6-3 6-2 3-6 6-0 in the last eight at Flushing Meadows.

Following his victory, Djokovic revealed that he was pleased with his response to dropping a set against the Russian.

"It was never going to be an easy match against Mikhail in the quarter-finals of a Grand Slam, and I was aware of his qualities and ability to come back," said Djokovic in a press conference.

"After I lost the third set I definitely tried to regroup and focus on every point individually and start playing the same game that I had in first two sets.

"It was important to get the early break in the fourth. I have done that, and after that I really felt a big relief on the court and just went for my shots and played great."

Djokovic will face Stanislas Wawrinka in the final four.