Serena Williams felt her hard work had paid off after claiming her ninth grand slam title in Sunday's US Open final.

The fourth-seeded American, who did not drop a set in the tournament, persevered through a tough second set to secure her first Flushing Meadows crown in six years with a 6-4 7-5 victory over second-seeded Serbian Jelena Jankovic.

"I've been working so hard all year," Williams said afterwards. "It's all paying off. I felt like I've been working the hardest, I should win."

The 26-year-old won the first set at a canter, putting the pressure on Jankovic with booming groundstrokes.

Jankovic, playing in her first final, took a while to get in the groove.

"Serena was a little bit better on the important points," Jankovic admitted. "I had my chances in the first set, and the second set as well, and I just (had) some unlucky points.

"I should have won them, but I didn't. I let my opportunities slip away.

"But overall, I was happy that I made it to the final, especially (because) I struggled a lot this year.

"I had a lot of injuries and all these problems, and I really worked hard to be here on this stage."