Novak Djokovic survived a highly taut, draining battle against Gael Monfils in the Shanghai Masters quarterfinals on Friday, rallying to win 6-7 (4), 6-2, 6-4.

Djokovic, the defending champion, looked out of sorts from the outset. The Serb hadn't been broken in his two previous matches in Shanghai, but he dropped serve twice in the first three games against Monfils.

After taking the first set, however, the 42nd-ranked Monfils struggled with pain in his abdominal muscles and couldn't break the Serb again.

Djokovic's semifinal opponent will be Jo-Wilfried Tsonga, a 6-2, 6-3 winner over Germany's Florian Mayer.

Juan Martin del Potro also advanced to the semifinals with a 6-3, 6-3 win over Nicolas Almagro and will meet either Rafael Nadal or Stanislas Wawrinka.

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