MIAMI (AFP) - Belarussian teenager Victoria Azarenka clinched the first major title of her career on Saturday by beating top seed and world number one Serena Williams 6-3, 6-1 in the Miami WTA hardcourt final. Williams, bidding to claim a record sixth title and third in a row, was badly affected by a left thigh injury which got worse as the match progressed. Despite the defeat, the American was already assured of hanging on to her world number ranking for the 71st week of her career. It was a poor quality final. The players reached 3-3 in the first set before Serena, who had defeated sister Venus in the semi-finals, began to feel her thigh which was heavily-bandaged and which was also supporting her knee. From that point on, the reigning US and Australian Open champion managed to win just one more game. Williams said she had been battling injury since her quarter-final victory over China's Li Na. "It was a little difficult moving to the left, and a little bit to the right. A little forward was also difficult," she said. The American said she almost would have preferred to lose to her sister Venus in the semi-finals, except that then she would not have kept her world number one ranking. "So that was the only upside to it," she said. "It was what it was. I gave the effort that I could give today. That's all I could give." And she had praise for her young opponent, who had retired ill against Williams after taking a set off the American in the Australian Open fourth round in January. "I think she has really, really improved," Williams said. "I actually look forward to playing her again so I can play a little better and obviously do better. "But I think she obviously has potential and she's going to be a really good player." Williams was under-powered on the court with five double faults, a poor 54-percent of first serves successful and an ugly 34 unforced errors. Azarenka tensed up as she served for the title. She double-faulted on her second match point before wrapping up the trophy on her third. "I was racked with fear," admitted the teenager. At 19, Azarenka claimed her first major title and third of her career which have all been won in 2009 with the previous two coming in Brisbane and Memphis. Her win here will elevate her to number eight in the world when the new rankings are released on Monday. "It was a great honour to meet Serena in the final and even greater to win against her," said Azarenka. "It's only this season that I have started to believe in myself and to believe that I can win tournaments."