Janko Tipsarevic a breath of fresh air

A slight air of negativity has surrounded the World Tour Finals the past few days, irrespective of Roger Federer's commanding performance against Rafael Nadal on Tuesday night.

Andy Murray, he of the often dour look, was forced to withdraw from the London event with a groin strain, and Nadal, Novak Djokovic and Mardy Fish have had health issues of their own.

It's a long, long season, as the players often remind us.

However, alternate Janko Tipsarevic's entrance Wednesday, replacing Murray, wasn't such a bad thing. The tattoo-laden, deep-thinking Serb is a real breath of fresh air.

And he's playing his best tennis -- despite falling 2-6, 6-3, 7-6 (6) to Tomas Berdych in a quality affair.

"I felt that I didn't disappoint anyone with my performance today," Tipsarevic said in his news conference.

Tipsarevic, regarded as an underachiever in the past, enjoyed a breakthrough season in 2011, winning his first two titles. Had he not been fatigued, Tipsarevic would have been in a better position in Paris to make a late push for a direct berth into the elite eight-man field.

Not only did Tipsarevic buck the odds by seeing action in London this week, but he seemed fortunate to land Berdych. Berdych was disheartened after wasting a match point and losing in a third-set tiebreaker to Tipsarevic's pal, Djokovic, on Monday evening, and he had struggled against the No. 2 Serbian.

Watching Tipsarevic stand in on the baseline, go for his returns, take the ball early and attempt more shots than usual down the line, you had to recall Nikolay Davydenko. Heading into Wednesday, Berdych held a combined 3-13 record against the duo, toppling Tipsarevic once, in Paris this month. Even so, Tipsarevic led by a break in both sets. Berdych, conversely, was 3-1 against Murray.

When Tipsarevic cruised in the first set, he was on course to become the first alternate to win a match at the tournament since another explosive shot-maker, Fernando Gonzalez, in 2005. Tipsarevic routinely rushed Berdych and protected his serve well; Berdych, meanwhile, carried his forehand woes into the opening set and got crunched behind his second serve.

But anyone who thinks the 2010 Wimbledon finalist is soft should think again. He's well past that, as he demonstrated when overcoming Murray in Paris in three sets. Berdych pumped his fist in the second set against Tipsarevic when he hung on to win a service game, evidence that he wasn't about to surrender meekly.

"I already showed it in the first match, all the way until the end, that I was feeling good on court," Berdych said in his news conference. "Today was pretty much the same. So I think my tennis is really, really good. Just enjoying to play. Going to keep fighting to try to go through."

What helped Berdych was his serve. Eight of his nine aces came in the final two sets, and he upped his percentage of points won on the second serve. The second serves were a little gutsier, and Tipsarevic dipped, minimally. Off the ground, he solidified.

Could Tipsarevic have done better on his match point at 6-5 in the tiebreaker? Probably. The backhand volley he was forced to hit wasn't overly low, although credit Berdych for making Tipsarevic hit the volley in the first place.

What likely will hurt Tipsarevic more, however, is the wild double fault at 6-6.

Indeed, he said afterward that he was "pissed."

If fit -- a twice-floored Tipsarevic injured his leg on the final point -- Tipsarevic figures to give Djokovic a test Friday, a la their U.S. Open quarterfinal.

"My right knee still hurts," Tipsarevic said. "We'll see what's going to happen when I cool off. But my feeling now is that I will be ready for practice [Thursday] afternoon."

On Wednesday, he and Berdych definitely provided a boost.