Serbian player Novak Djokovic returns a forehand during his win over US player Mardy Fish in the men's final at the Pacific Life Open at the Indian Wells Tennis Garden in Indian Wells, California on March 23, 2008. (UPI Photo/ Phil McCarten)

Nadal must finish one round better than Djokovic in Hamburg, Germany, to keep his No. 2 ranking. They are one a collision course for a semifinals matchup after their wins at the clay-court event.

Nadal, seeded second, took a step in that direction with a 6-3, 6-2 win over 15th-seeded Andy Murray while Djokovic, seeded third, defeated Croat Ivo Karlovic, 7-6 (7-3), 6-3, in third-round play.

Djokovic needs to get by Albert Montanes, who advanced with a 6-2, 6-1 rout of Janko Tipsarevic, in Friday's quarterfinals to get a possible shot at Nadal on Saturday. Nadal needs to beat 11th-seeded Carlos Moya, a 6-2, 6-7 (3-7), 6-1 third-round winner over Marat Safin, for a chance to hold onto the No. 2 spot.

Both are well behind the ranking total of world No. 1 Roger Federer, who topped Robin Soderling, 6-3, 6-2, and on Friday meets Fernando Verdasco, who upset No. 5-seeded Davis Ferrer, 7-6 (7-4), 6-2, on Thursday.

Friday's fourth quarterfinal has crowd favorite Nicolas Kiefer playing Andreas Seppi. Kiefer upset No. 4 Nikolay Davydenko, 7-5, 6-3, while Seppi eliminated 12th-seeded Juan Monaco 6-0, 6-3 in third-round matches.