* Radwanska to play Cibulkova in Sydney final
* Ferrer reaches Auckland semis
* Berdych beaten by Hewitt at Kooyong (updates with later matches)
SYDNEY, Jan 10 (Reuters) - Agnieszka Radwanska needed eight match points to finish off Li Na on Thursday but confirmed her fine pre-Australian Open form by maintaining her perfect start to the year and reaching the final of the Sydney International.
The Polish top seed was well worth the 6-3 6-4 win over her Chinese opponent and will face Dominika Cibulkova in Friday's final after the Slovakian stunned German second seed Angelique Kerber 6-2 4-6 6-3.
"I think I was really playing good tennis the last couple of days," said Radwanska, who also won the Auckland Classic last week and has started the year with eight straight wins. "I hope I can continue playing at this level."
David Ferrer has played six fewer matches than Radwanska this year but really hit his stride on Thursday when he swept aside Lukas Lacko 6-2 6-1 to remain on course for a fourth title at the Auckland Open.
The Spaniard, who like Radwanska will be seeded fourth at Melbourne Park next week, needed just 54 minutes to beat his Slovak opponent and set up a semi-final against France's Gael Monfils, who later beat Tommy Haas 3-6 7-5 6-3.
The fifth seed in the men's draw for the year's first grand slam, Tomas Berdych, had a less enjoyable day down at Kooyong where he was humbled 6-3 6-2 by Australia's resurgent former world number one Lleyton Hewitt.
Hewitt, now 31 and ranked 82nd in the world, beat Milos Raonic in his first round robin match on Wednesday and his 88-minute victory over Czech Berdych puts him into the final of the exhibition event.
There he will meet either Argentina's world number seven Juan Martin Del Potro or Cypriot Marcos Baghdatis, who face off at the Kooyong Classic on Friday.
"I'm just thrilled to be able to perform like this against quality players and on back-to-back days," Hewitt told reporters.
"I've had five tough sets in two days and that will hold me in good stead for next week."
Although Radwanska has had a busy schedule, Li was clearly tired after playing nine times in 10 days as well as flying from China to Australia after winning last week's Shenzhen Open.
The Pole broke on Li's first service game and rarely looked back before stuttering to close out the match as she had in beating Yanina Wickmayer in Auckland last week.
"It was kind of like a deja vu from Auckland final," she said. "I'm really ready for the Australian Open. I will do of course everything to win that match tomorrow as well, and we'll see. I hope to win 16 matches in a row."
Cibulkova added world number five Kerber to her list of top 10 victims in Sydney this week having already beaten Petra Kvitova and Sara Errani.
Like Hewitt, Australian young gun Bernard Tomic proved he was a player to be avoided in Friday's draw for the Australian Open with a quarter-final victory.
The 20-year-old came from a set down to beat defending champion Jarkko Nieminen 6-7 6-4 6-2 and extend his winning streak to five matches this year, including his stunning victory over Novak Djokovic in Perth last week.
"I'm really confident now, and I got a shot to get into the final for the first time in my career," said Tomic, who will play Andreas Seppi in the semi-finals after the Italian third seed beat Marcel Granollers 6-4 7-5.
Frenchman Julien Benneteau earlier cruised past American qualifier Ryan Harrison 6-4 6-2 and will play Kevin Anderson for a place in the final after the South African had an equally emphatic 6-4 6-3 win over Denis Istomin of Uzbekistan.
Men's top seed John Isner, who lost to Harrison on Wednesday, pulled out of the Australian Open on Thursday because of a knee injury, leaving Sam Querrey as the only American men's seed at Melbourne Park.
Querrey overcame Canada's Jesse Levine 6-4 7-6 in Auckland and will face Philipp Kohlschreiber in the semi-finals after the German beat Xavier Malisse 7-6 6-4. (Editing by Justin Palmer)