By Simon Evans

MIAMI (Reuters) - Andy Roddick could emulate Andre Agassi and enjoy his greatest success in the latter years of his career, his coach Larry Stefanki said after watching the American win the Sony Ericsson Open Sunday.

"I think this is still the infancy, I really do, I think he could be similar to Agassi where his best years are from 27 onwards," he told reporters.

"I have seen it done before. I think he was very raw and his game is starting to come to where it is not hit and miss."

So far this year Roddick has won the Brisbane Open and was the beaten finalist at Indian Wells as well as triumphing for the second time at Key Biscayne.

Despite possessing a tremendously powerful serve, Roddick has been something of an underachiever as he won his solitary grand slam at the 2003 U.S. Open.

But Stefanki believes Roddick now has a more diverse set of skills at his disposal.

"He has a lot of things to fall back on to win when he is not playing great, he does have the best serve in the game at the moment, day in day out, but if you add all the other components, the slice and so on, it puts him in a different echelon," he said.

As well as the technical adjustments that needed to be made to Roddick's game, Stefanki said weight loss, a better tactical approach and reduced off-court stress have been key elements in the player's rise.

The coach said Roddick has also changed his diet -- ditching his junk food habits for more organic options, helped by his swimsuit model wife Brooklyn Decker.

"I told him 'If you want to get faster, you have to lose weight'," added Stefanki, who began his career working with John McEnroe.

Roddick said he was delighted with his relationship with his coach, who quickly laid down the ground rules.

"I think he wanted to run things and I was more than okay with that, that's what I wanted. I wanted the guidance.

"I'm not going to pay a guy to be my coach and then tell him what to do. You would be surprised how prevalent that is in tennis.

"It's a great mix. I love his tennis IQ. I like his energy. I don't know if I've ever seen him stressed out unless we're late for a tee time.

"The tennis side of it works and the personality side of it works. So I think we're in a good spot," he said.

(Editing by Pritha Sarkar)