(Reuters) - Australian Open champion Angelique Kerber cooled off red-hot Simona Halep in straight sets on Saturday to reach the final of the Southern & Western Open in Cincinnati and move one win away from taking over as world number one.

Second seed Kerber beat the third-seeded Romanian, winner of 13 successive matches, 6-3 6-4 to set up a Sunday final against Karolina Pliskova.

The German needs to beat Pliskova to end Serena Williams' 183 successive weeks as world number one.

The American is three weeks short of Steffi Graf's all-time record, but the 28-year-old German can make her own history with a win on Sunday.

"I have still, one match to go," said left-hander Kerber, fresh off winning the Olympic silver and the Wimbledon runner-up to Williams last month.

"I would not think about this the whole week. Everybody's asking me about that. If it happens, it will be amazing, but still I have to focus on the next match against a real tough opponent, Pliskova."

The big-serving Pliskova, the 17th-seeded Czech, swept past French Open champion Garbine Muguruza of Spain in a dominant performance, winning 6-1 6-3 in the earlier semi-final.

Kerber leads her head-to-head against Pliskova 4-2, with the Czech's last win coming in last year's semi-finals in Sydney.

Kerber was locked in a tight first set in breezy conditions against Halep when rain forced a 30-minute delay.

Once they resumed, with Halep serving at 3-4, the Romanian was ice-cold, particularly off the backhand, and Kerber dominated.

The German broke Halep when a backhand sailed wide, held serve to finish the first set, then swept to a 4-0 lead in the second.

Halep, with her back to the wall, cut loose and began finding her range with aggressive swings from both wings and won the next three games.

The Romanian was within a point of taking the 10th game to deuce in her quest to bring the set back on serve, when Kerber broke a string on her racquet and a startled Halep mis-hit her backhand return wide to end the match.

Pliskova, who has won five WTA titles, was in full command in her semi-final, belting 17 winners and five aces.

She needed just an hour to clinch victory.

"I know I beat (Muguruza) in the last two matches, so I knew it's going to be tough for her to beat me if I play well or if I play solid," Pliskova said in a courtside interview.

"I was not thinking about that she's a French Open champion. This you cannot take on the court."

(Reporting by Larry Fine in New York; Editing by Andrew Both/Greg Stutchbury)