Serena Williams of the US hits a return to Sorana Cirstea of Romania during their women's final tennis match of the Rogers Cup tennis tournament in Toronto, Aug 11, 2013. [Photo/Agencies]

Even though she did not drop a set in winning her eighth title of the season at the Rogers Cup on Sunday, Serena Williams believes she can play even better heading into the US Open. [More about US Open hard court season]

"Definitely can do a lot more," she said after her 6-2 6-0 victory over Romania's Sorana Cirstea in Sunday's final.

"It's always about constantly improving and never saying I did great and I can be satisfied.

"It's like I did great but what can I do better? What can I improve on? That's what I always strive for."

Williams won the French Open in June and has lost just three matches all year but the 31-year-old said her defeats to young American Sloane Stephens at the Australian Open and Germany's Sabine Lisicki at Wimbledon had reminded her she needs to manage her on-court attitude.

"That could improve," she said. "I get so intense and so emotionally charged, and I want it so bad that sometimes it works against me."

Cirstea discovered first-hand just how motivated Williams is when she faced the ruthless world number one on Sunday and the unseeded Romanian said she was impressed by what she saw.

"She knows when to raise her level," Cirstea said. "She knows when it's enough to play and when she has to step it up."

Williams rebounded from her shock loss to Lisicki at Wimbledon by winning a tournament in Sweden but was still unhappy at the way she played so returned to Florida to continue working with her coach, Frenchman Patrick Mouratoglou, and her father.

"I was really disappointed in how I played the last month," she said. "Even though I won Sweden, I was not happy with the way I played.

"So I went home and was working with my dad a lot and just going back to the basics. I didn't show it so much in (Toronto). Hopefully I can continue to bring that game out."

Her victory on Sunday was Williams' 54th career WTA singles title, elevating her to outright fifth on the all-time list.

Despite her incredible record, the American said she was still suffered from nerves and expected to have more when she starts her US Open defence last this month.

"I think it almost is exciting to have butterflies, because it means that you care about it so much and you still get nervous," she said.

"I think when the day comes and I'm not nervous and don't have butterflies, then I need to start rethinking what I'm doing."