Tennis is a game of streaks, of rallies, of momentum.

When you’re rolling, it’s easy to keep it up. When you’re doing poorly, it’s difficult to turn things around.

Unless, of course, you’re Tommy Haas.

Haas, who defeated Nicolas Kiefer 7-6 (6), 6-4, in the finals of yesterday’s Mercedes-Benz Cup at the Los Angeles Tennis Center, didn’t exactly have the look of a champion early in the match. But he certainly turned it around in grand fashion.

Down 5-1 at one point in the first set tiebreaker, Haas looked dejected, a player simply being beaten by a better man.

Though it would have been easy for Haas to pack up and regroup for the second set, he did nothing of the kind. Instead he went on to win six of the next seven points, take the tiebreaker, the set, and effectively steal the momentum that pushed him through to the championship.

“The tiebreaker was extremely high-quality tennis, and it was an important first set,” Haas said.

That’s quite an understatement from the German, who won his second tournament this season after sitting out for 16 months with shoulder problems.

Sunday’s result was mildly surprising simply because it was Kiefer who seemed to seize control at the outset. Playing in the first all-German final in 10 years, Kiefer raced out to the lead in the tiebreaker. He definitely looked the stronger player, dictating points and frustrating Haas with his power and precision.

Then it all changed. Kiefer had his chances, many more chances, in fact, but he once again walked away winless in a finals appearance, the sixth consecutive time he has done so.

“I had many, many opportunities,” Kiefer said. “I just couldn’t make them count.”

It was a day of missed chances for Kiefer, who at one point was ranked as high as No. 4 in the world in 2000. In the second set he had a triple-break point, but Haas fought off every one, eventually winning the game. This championship is the seventh of Haas’ career and the second of his “new” career, he said.

After undergoing two shoulder surgeries and intense rehabilitation, Haas began this tennis season with what he thought were reasonable expectations: One was to crack the top-100 in the world; the other was to win one tournament.

Consider those done and done. And done.

He’s already gone above and beyond, reaching the top 100 weeks ago and emerging victorious in two tournaments so far.

“It’s just proof that if you fight hard, it’s still possible to have some success,” said Haas, whose career-high ranking was No. 2 in May 2002.

But the journey certainly wasn’t easy. There were days when he simply threw in the towel. Frustrated with the pain and an inability to compete, Haas would step away, travel, and try to forget about things.

But now he’s back – with a vengeance.

Sounds kind of like the Terminator. Or the Governator.

After Sunday’s match Haas was headed to Gov. Arnold Schwarzenegger’s Pacific Palisades home to dine with the action star because Haas’ father attended grade school with Schwarzenegger’s father in Austria. He wouldn’t say whether his invitation was contingent upon a victory in the final.

“I’m going to have to ask him,” Haas said with a laugh. “If it is, that’s pretty big motivation.”

After the match Haas and Kiefer could agree on a lot of things. They both felt the day was good for German tennis, and each thought the other deserving of the championship.

“I think it’s sad that you have to say there’s one winner and one loser,” Kiefer said. “We both deserved to win.”

Kiefer and Haas, who are friendly off the court, agreed on one more thing.

Both campaigned for the tournament’s winner to receive a new Mercedes-Benz, which would mimic the prize awarded to the winner of the Mercedes-Benz Cup in Stuttgart, Germany.

“I just talked to (Tournament Director) Bob (Kramer) and tried to change it for next year,” Kiefer said with a smile.

Kiefer also promised to be back, as he has improved in each of the three years he has played this event – first a quarterfinalist, then a semifinalist and now a finalist.

He seems to be gaining momentum. But he learned Sunday how quickly it can change.

Just ask Tommy Haas.