MIAMI, March 27: Switzerland’s Roger Federer moved into the quarterfinals of the Nasdaq-100 Open Masters Tuesday when fifth seed Tim Henman of Britain retired from their fourth round clash with a sore neck as he trailed 6-2.

At the end of the opening set, Henman, in obvious discomfort called the trainer on to the court for treatment.

After working on the neck for several minutes the world number six got up and shook hands with his Swiss opponent, who he had beaten in all four of their previous career meetings, and left the court.

After the opening game of the match, Henman’s neck began to stiffen prompting him to call the trainer for treatment.

Meanwhile, second seed and defending champion Venus Williams beat the rain and Elena Dementieva, winning 5-7 6-3 6-2 to set up a potential semifinal showdown with sister Serena.

Williams suffered a first set lapse, squandering a 5-3 lead as the 12th-seeded Russian stormed back to win the next four games to seize control.

But the Wimbledon and U.S. Open champion rallied to take the next two sets in workmanlike fashion to reach the semifinals for the fifth time in six events this season.

A win by the younger Williams would set up the seventh career meeting between the tennis siblings and the first since they clashed in the final of last year’s U.S. Open.

Venus holds a commanding 5-1 lead over her sister.

Results (x denotes seed):

MEN (fourth round): Andre Agassi (USA x9) bt Thomas Johansson (Swe x8) 7-5, 6-2; Roger Federer (Swi x12) bt Tim Henman (Gbr x5) 6-2 retired; Nicolas Lapentti (Ecu) bt Adrian Voinea (Rom) 6-2, 3-6, 6-3; Juan Ignacio Chela (Arg) bt Gaston Gaudio (Arg) 6-1, 5-7, 4-3 retired; Lleyton Hewitt (Aus x) led James Blake (USA) 6-4, 3-1 (postponed, rain)