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American sprinter Tyson Gay was unbeaten in the 100m last season but says he will have to improve to challenge rival Usain Bolt.

Gay, 28, finished last season as world number one as he also handed Bolt a first loss in two years in August 2010.

"I have to step it up a notch when I take Bolt on," said Gay, who will start the current campaign with a 150m race in Manchester on Sunday.

"It means I have to be sharp and ready to run because this guy is no joke."

Gay clocked the fastest time of 2010 with 9.78 seconds and beat Olympic and world champion Bolt when the two met in Stockholm last year.

But, with the pair scheduled to contest the World Championships in Daegu, South Korea in August, Gay has refused to get carried away by the win over Jamaica's Bolt, who also holds the world record time of 9.58secs.

"Last year couldn't have gone any better. I had a great season, I enjoyed my victories, I enjoyed my big victories," said Gay.

"But in this era of track and field it's about running super-fast.

"Last year was last year. I know I have to work even harder this year and be smarter. I don't really think about last year.

"It's a new year and I have new goals and I want to win. That's it."

Gay can set a marker with his outing in the 150m in Deansgate at the Great City Games in Manchester this weekend in a race also including British duo Marlon Devonish and Christian Malcolm as well as Portuguese veteran Francis Obikwelu.

Bolt set a time of 14.3s over the distance at the inaugural 2009 meeting and Gay said: "I know the record is 14.3 and that's amazing, that is fast.

"I'm not in 14.3 shape, but I'm looking forward to trying to run a good time.

"I've had a couple of little injuries here and there, so I'm just trying to see where I'm at."