Second-seeded Venus Williams was knocked out of the Nasdaq-100 Open 6-3, 5-7, 7-6 by Russia's Elena Dementieva in the quarter-finals on Wednesday as the American battled to shake off a foot injury.

Dementieva, the fifth seed, got off to the more consistent start and could have won in straight sets but failed to close out when serving for the match at 5-4 in the second.

Williams was hindered by a foot injury two games later at 6-5 and 30-30 when she landed awkwardly after a forehand.

The American was forced to take a three-minute injury time-out while she received treatment and had the foot heavily strapped by WTA trainer Lisa Heller.

Despite the injury, Williams got to set point in the next game and levelled the match when Dementieva's forehand was long.

"After the medical break I was thinking she was a good actress because she was moving so much better than before," said Dementieva.

The Russian's concentration faltered as Williams broke again at the start of the third set and while Dementieva retrieved the break Williams had a chance to serve out the match at 5-3.

Four double faults in that game let Dementieva back in and the Russian finally sealed victory in the tie-breaker, taking her first match point when a Williams's forehand sank into the net.

The Nasdaq-100 Open is Williams's fourth tournament of the season and she has yet to get past the quarter-final stage after missing the second half of last year with abdominal injuries.

Dementieva will play either compatriot Nadia Petrova, seeded eight, or Frenchwoman Nathalie Dechy in Friday's semi-finals.