Melbourne: Unseeded after an injury-plagued 2006 that limited her to four tournaments, former world No 1 Serena Williams reached her first Grand Slam final in two years on Thursday, beating Nicole Vaidisova 7-6 (5), 6-4 in the Australian Open semifinals. Standing in the way of an eighth Grand Slam title is top-seeded Maria Sharapova. Sharapova turned her semifinal against No 4 Kim Clijsters into an Australian farewell match for the 23-year-old Belgian, who is retiring at the end of the year, with a 6-4, 6-2 victory. Williams and Sharapova are 2-2 in head-to-heads. Williams won their last encounter after saving match points in the semifinals here two years ago before going on to win the title. Vaulting up in rankings Ranked No 81 coming into the tournament after dropping out of the top 100 last year while dealing with a bad knee, Williams guaranteed herself a return to the top 20. "I can't believe it," she said. "That's awesome. I'm like a chameleon. I can kind of change and get my game going to whatever the situation is. If I play well, which I don't think I've even reached yet at all in this tournament. It's really hard for anyone on the women's tour to beat me." Sharapova certainly isn't taking Williams lightly. "I'm going to be playing against a player that didn't really expect too much coming into this tournament," she said. "She's playing some really good tennis. I think she has nothing to lose going into the match. Those are always dangerous opponents," she added. As she has throughout the tournament, Williams took time to heat up. Although she didn't look as sluggish as in her last match, she still watched a number of Vaidsova's stinging groundstrokes whiz by for clean winners. Williams sprinted ahead 4-0 in the tiebreaker, then doubled-faulted on consecutive points as Vaidisova leveled at 5-5. Grunting louder with each shot, Williams whacked a backhand cross-court winner for set point, then growled loudly when Vaidisova then hit a forehand into the net. Williams ran off four straight games to pull ahead 5-1 in the second set. A quick finish seemed certain. Then came the comeback that fell just short. Vaidisova broke Williams as she served for the match to pull within 3-5, then fell behind 0-40 for triple match point in the next game. The Czech fought back to deuce, fended off another match point, then held to a thunderous ovation. "I almost did a gagarooney there," said Williams, explaining: "Basically, you know gagging." Serving again to finish it off, Williams had match point number 5 at 40-30, only to see Vaidisova whip a backhand crosscourt winner on the line. Williams thought the ball was out and started to celebrate, then clearly wanted to question the no-call but had no challenges left after using up her allotment earlier. Her 10th ace of the match, on a second serve, set up match point No 6, and Williams finally cashed this one, throwing her hands in the air and leaning back to look at the sky. "She's definitely a great champ," Vaidisova said. "She played the tight points very well. I had my opportunities. I didn't use them. That was the big difference. I was trying to go for a winner or easy shot too early." Dominant Sharapova ÃÂ Sharapova, last year's US Open, wasn't at the top of her game either, committing eight double faults, missing badly on a number of easy putaways and finishing with six more unforced errors (33) than winners (27). But she was at her best under pressure, fending off seven break points in the second set. "I felt like I played a much better match all around today," Sharapova said. "Couldn't quite get the serve and return together in the beginning. But overall I was really focused. I did the right things at the right time. I was patient when I had to be patient, played a smart game." It helped that the normally solid Clijsters was even more inconsistent, and her worst errors came at the worst times as she squandered opportunity after opportunity. She frequently forced Sharapova to hit two or three good shots to win a point, but had only two winners of her own in the last set. Sharapova broke Clijsters to go ahead 2-0. The Belgian could never get back into it with mistakes that had fans groaning. She double-faulted while serving at 2-5 to set up match point. Sharapova finished it off with a crisp forehand winner, then blew kisses to the crowd. Clijsters got two standing ovations as she said goodbye to Rod Laver Arena. "I have so many great memories from here," she said. "I'm going to come back tomorrow and take my time to say goodbye to everybody, just get everybody's e-mail address, number."