David Ferrer eased into the semi-finals of the Erste Bank Open as Kevin Anderson and Ivo Karlovic suffered surprise exits.

Top seed Ferrer, who occupies the eighth and final spot at the ATP World Tour Finals, needed only an hour and 14 minutes to see off eighth seed Fabio Fognini in Vienna.

The Spaniard lost only 12 points on serve and faced just two break points on his way to a 6-4 6-2 win, which sets up a last-four clash with Gael Monfils.

Sixth seed Monfils was forced to come from behind to earn his semi-final spot, defeating Lukas Rosol 6-7 (3-7) 6-3 6-3.

Monfils lost a first set - in which neither man faced a break point - on a tie-break, but fought back to progress thanks in part to 19 aces.

But neither Anderson nor Karlovic will be joining Ferrer and Monfils in the semis. Second seed Anderson was beaten in three sets by Steve Johnson and seventh seed Karlovic lost in straight sets to Ernests Gulbis.

Johnson prevailed 5-7 7-6 (7-5) 6-4 after two hours and 37 minutes, despite Anderson serving 23 aces.

Karlovic's big serving was not enough to prevent him from suffering elimination as he lost two tie-breaks against Gulbis, who came through 7-6 (7-4) 7-6 (7-5).