After a two-month absence to nurse a painful back injury, American icon Andre Agassi looks as sharp as ever.

The top-seeded Agassi defeated Gilles Muller of Luxembourg 6-4 7-5 on Sunday to claim his fourth Mercedes-Benz Cup title - and first win this year.

"It's pretty exciting for me because these moments don't come by to often and it seems they're getting less and less as I get older," Agassi said.

"But it feels amazing to be out here, to be eager, to be playing the sport in the time of my life when I can enjoy it. Not just for me what it means to me personally, but it's a great platform for the summer."

The 35-year-old was playing his first tournament since the French Open due to a sciatic nerve problem caused by a bulging disc in his back, but he looked strong all week, dropping just one set en route to recording his 60th career tournament win at the US$380,000 hardcourt event.

"It's been a tough few weeks in many respects but a great one in others," Agassi said.

"We put aside a lot of questions, we've gotten back to what makes things tick out here. And just to see the hard work pay off feels great."

Agassi, who earned US$52,000, joined Jimmy Connors, Frank Parker and Roy Emerson as the only players to win this event four times. He improved to 60-28 in ATP Tour finals and 34-6 all-time in this event.

The 22-year-old Muller had saved two match points in his semi-final upset of second seed Dominik Hrbaty of Slovakia on Saturday night.

"He has an unbelievable ability to hit one good shot, maybe two," Agassi said of Muller.

"If you can fight that off, then at the end of the day he's playing low-percentage (tennis). That's what I did better today and I was defending better. He upped his game in the second set and started playing more aggressive, but even so I was pretty comfortable."

Ranked 75th in the world, Muller stunned Agassi in the Washington semi-finals last year en route to his sole prior final appearance, where he lost to Lleyton Hewitt.

But Muller was overmatched in this one by the eight-time Grand Slam champion, who took the opening set after recording a break in the first game and yielding just two points on his own serve.

In the second set, Muller held a 5-4 lead and earned a set point on Agassi's serve in the 10th game. But at 30-40, he sent a second-serve return into the net and Agassi eventually held to level the set.

In the 11th game, Muller jumped out to a 40-0 lead but watched helplessly as Agassi reeled off five straight points to secure the set's lone break. At 6-5, Agassi ended the match with a crosscourt forehand winner to the delight of the crowd of 7,027 at the UCLA Tennis Center.

As a result, top seeds improved to 18-0 in finals this year, while unseeded players fell to 2-16.

The year-end number one junior in 2001, Muller's best result this year prior to this week was a quarter-final finish in Casablanca.