"I surprised myself in many ways," the German said from his Bradenton, Fla., home in an interview with ESPN.com. "I have a different outlook than five, 10 years ago. I'm not looking forward too far down the road. I'm thankful for every match I win, every chance I get to go out and compete.
"Some of these tournaments I'm playing, I think maybe it's for the last time. Maybe not."
Maybe not. Haas who turns 35 in a week, stunned No. 1-ranked Novak Djokovic 6-2, 6-4 in a fourth-round match here at the Sony Open on Tuesday night.
Haas is the second-oldest man ever to take down a world No. 1. (Gianluca Pozzi was a few days closer to 35 when Andre Agassi retired with a back injury in Queens in 2000.) To underline the significance of this victory, consider that Haas' only other win against the ATP World Tour's top-ranked player came nearly 14 years ago against Agassi.
"This is what you play for -- what I play for," Haas said afterward. "These are the moments I appreciate the most, going on those big stadiums, big stages, playing against the best people in the world.
"Playing against someone like Novak and coming out on top at this time of my career, it's unbelievable."
While Djokovic, No. 2 Roger Federer (who is 31) and No. 4 Rafael Nadal aren't in their accustomed spots in the quarterfinals here, the old men are out in force. Joining Haas in the two quarterfinals in the top half of the draw are Jurgen Melzer, who turns 32 in May and David Ferrer, who hits 31 next Tuesday. The youngster in the group? Frenchman Gilles Simon, who is merely 28.
It's the first time in a decade that three 30-year-olds made the quarters here.
Is 30 the new 20 in men's tennis? It sure looks that way. There are no teenagers in the ATP World Tour's top 100, but there are 26 30-somethings. Haas is the oldest man in the top 50 and the second-oldest in the top 100. Less than a year ago, Federer won his seventh Wimbledon title at the age of 30.
"It's a combination of things," Melzer said a few days ago. "Guys are in better shape and are willing to stay out here longer."
And the financial incentives are far greater than they used to be. Melzer, for example, lost more singles matches last year than he won (20-25) and still managed to collect $917,106 in prize money. He says he'll stick around as long as he feels he can continue to play credibly.
Haas, meanwhile, seems to have bought himself a little more time. Older athletes often say that their mental prowess, their vast experience, helps compensate for their deteriorating physical condition. On Tuesday night Haas was flying around the court and, at the same time, playing a superb tactical match.
"He was the better player, no question about it," Djokovic said later. "The results show everything. As far as I'm concerned, it's definitely the worst match I have played in a long time. I just didn't feel good on the court."
It was only the second loss of the year for Djokovic; he won his first 17 matches (including all seven at the Australian Open) before falling to Juan Martin del Potro in the semifinals at Indian Wells.
The blustery conditions, Djokovic said, were more conducive to Haas' style of play. These were some of the coldest conditions in which he's ever played.
"Basically no air in the balls, didn't bounce at all, which is more suitable to his game," Djokovic said. "He has quite flat shots. He used the variety really well."
Hitting a slice on the backhand side more often than topspin, Haas crashed out to a 6-2, 3-1 lead. Playing quickly, light-blue hat backward on his head, Haas looked a lot like the 23-year-old who won four titles in 2001.
Djokovic, fighting off a number of break points, got it back to 4-all. At one point, Haas lost eight consecutive points and you wondered whether he was going to surrender the match to a player who had beaten him four times in six tries.
But Haas broke Djokovic when he sent a forehand wide and then slipped into net and cracked a backhand volley winner.
Sitting in the changeover chair, looking straight ahead, his legs jiggling like mad, you could see how much it meant to Haas. When the last forehand went cleanly through the court, he looked stunned.
Haas' legs may feel a little heavy Wednesday, but he's got more work to do. He is into the quarters in both singles and doubles (with Belgian Xavier Malisse) for the first time in an ATP Masters 1000 and will play two matches.
In that recent interview with Haas, he was asked how long he planned to continue playing.
"As long as I'm enjoying myself, physically and mentally, and have some success here or there, I'll continue," he said. "For sure, the rest of the year and maybe a year after that. One of my goals is for my daughter to see me play and realize what her dad's doing. She'll turn 2 in the fall and get an opportunity to see some tournaments later this year. That means a lot to me.
"There will be a point when it is taken away from me, and then there will be a lot of other choices for me. Until that time, I'm just going to ride it as long as I can."