MADRID: Novak Djokovic blasted the ATP rankings system as "cruel" on Wednesday and vowed to reclaim his world No 3 spot from Andy Murray.

"It really motivates me even more to get back to the third spot or even go a step further," said the Serbian, who has reached the last three Masters 1000 finals (Miami, Monte Carlo, Rome) but fell to fourth in the world behind Murray on Monday.

"I try not to pay too much attention to the rankings, but to be realistic, playing three Masters Series finals in a row and winning a 250 event (Belgrade) is incredible success - even if you are dropping a spot down in the rankings.