By Peter Simpson

BEIJING (Reuters) - Czech Tomas Berdych won with an ace to sink ruffled first seed Jo-Wilfried Tsonga 6-4 4-6 6-1 on Saturday and set up a Beijing Open final against Marin Cilic after he triumphed in a battle of the Croat big servers.

Tournament favorite Tsonga was seeking to build on his recent win at Metz but the Frenchman repeatedly sent back wild returns.

The annoyed world number seven at times blamed the balls but the umpire's indifference unsettled the Wimbledon semi-finalist, whose errors proved costly despite some exquisite rally wins and powerful baseline shots.

Berdych, who needed his left ankle re-strapped in the third set, proved the hungrier of the pair and kept his nerve to edge his opponent and break serve twice, booming an ace to seal the contest.

"I thought I was in with a pretty good chance. This match could really change my season from being a good one to a really good one. Marin Cilic is another tough opponent, so I'm expecting a really tough match tomorrow," world number 10 Berdych told reporters.

The 26-year-old will meet Cilic in Sunday's final at the newly-opened Center Court at China's National Tennis Center after the Croat relied on a dominant serve to beat compatriot Ivan Ljubicic 6-4 6-3.

Cilic, the losing finalist two years ago, said his game really got going when he got the first break against Ljubicic.

"When that first break came I started to serve better and the beginning of the second set was really crucial," the 23-year-old said.

"He had few break points and I started to serve maybe the best that I ever served."

In the women's draw, Andrea Petkovic produced a clinical 6-2 6-0 victory over Romanian Monica Niculescu to set up a final against Agnieszka Radwanska after the Pole beat Flavia Pennetta.

Italian Pennetta could not rekindle the blistering form that saw her take out world number one Caroline Wozniacki in Friday's quarter-finals and slumped to a 6-2 6-4 defeat.

(Editing by Peter Rutherford)