Defending champion Novak Djokovic got his Madrid Open title defence off to a winning start on Tuesday, but he was made to work for it in his second-round match by Daniel Gimeno-Traver.

371242 - Unhappy Djokovic sneaks into third round

Djokovic, who beat Rafael Nadal in last year's final, has been one of several players to question the highly controversial blue clay in Madrid. And he may find more cause for complaint after he looked uncertain on the surface - said to be less trustworthy under foot than the traditional red dirt - during his 6-2 2-6 6-3 win over the world No. 137.

Gimeno-Traver surprisingly created the first break chances of the match in Madrid, wasting two in Djokovic's opening couple of service games. Instead it was Djokovic who gained control, converting at the third attempt in the fourth game for a 3-1 advantage.

A second break ensured the first set belonged to the world No. 1, who continued to use his trademark angles to force Gimeno-Traver consistently onto the back foot.

The expected victory march did not materialise, though, with Gimeno-Traver the dominant force in the second. With Djokovic's serving statistics dropping, the Spaniard leapt all over his second serve for two breaks to level the match.

Djokovic repeatedly shook his head in the direction of the court, earning a reprimand at one point from the umpire, and the decisive third set went with serve until the sixth game. At that point the Serb forced his rival to defend a number of break points, eventually finding the breakthrough before serving out for the match.

Former French Open semi-finalist Tomas Berdych is also into round three after he beat Kevin Anderson 6-4 6-3. Berdych hit 11 aces and broke twice in a solid display of power hitting.

Juan Martin Del Potro, fresh off his triumph at the Estoril Open, confirmed his presence as a contender in Madrid, beating Florian Mayer 6-4 6-2 in the first round. The Argentinian enjoyed the fast pace of the court as he smeared a range of forehand winners past his opponent, completing victory in 76 minutes.

No. 13 seed Feliciano Lopez was the biggest faller on Tuesday, losing 3-6 7-6(6) 6-4 to Jurgen Meltzer. Both men delivered 10 aces in a match that saw Lopez win more points, but it was the second-set tiebreaker that proved crucial as each player won a set either side.

Elsewhere, ninth seed Gilles Simon needed two-and-a-half hours to see off Italian Fabio Fognini 6-7(1) 6-3 6-3, Simon's countryman Gaels Monfils also went to three sets in a 7-5 6-7(2) 6-3 win over Philipp Kohlschreiber, and rising star Milos Raonic beat David Nalbandian 6-4 6-4.

There were also notable wins for Fernando Verdasco, Alexandr Dolgopolov, Richard Gasquet, Stanislas Wawrinka and Marin Cilic.