MELBOURNE: China's Li Na concedes her serve needs more work if she is to achieve her goal of breaking into the world's top five after losing in the Australian Open semifinals yesterday.

The 16th seed was speaking after going down to defending champion Serena Williams 7-6 (4), 7-6 (1) in a two-hour thriller at Rod Laver Arena.

Williams blasted down 12 aces in the match against Li's one, one of those coming on set point in the first set and another on match point.