Like the proverbial bad penny, the San Antonio Spurs keep showing up. Unlike the proverbial bad penny, this should be construed to be a good thing.

Despite obvious warts and blemishes, the Spurs on their good days still represent the best of what the NBA occasionally offers, even if the great unwashed out there doesn’t always recognize it. (See: television ratings when the Spurs are in the NBA Finals. Or: Network execs consider hemlock.) When they are on their game – and, in case you missed it, they are – they showcase balance, teamwork, an unflinching commitment to defense, a wise-cracking head coach, arguably the game’s most gifted power forward in Tim Duncan and the eternally entertaining Manu Ginobili.

Building momentum for the playoffs has been a rite of spring for the Spurs ever since Duncan fell into their laps in the 1997 lottery. In years past, they have used a blistering March to pull away from the pack or to solidify their hold on a high playoff spot in the Western Conference. This year, it’s different.

They are neither a division leader nor, at the moment, a team which can even claim homecourt advantage in the first round of playoffs (something they have had every year since 1999.) But that could very well change if they continue to play in April the way they have played in March.

“Right now, we are playing our best basketball of the season, thankfully,’’ said their coach, Gregg Popovich.

That was 90 minutes before his team went out and destroyed the Celtics in Boston, holding them to a season-low 73 points.

“We’re starting a little later than usual, but we’re finally becoming a basketball team. For a lot of the year, for a lot of reasons, we were all over the map.”

They were indeed. At one point during the season, the Spurs lost an unthinkable 10 of 16 games. They’ve already lost more games (28 going into Monday against the Nyets) than in nine of the 12 seasons in which Duncan has been their anchor and foundation. (One of those seasons was the 50-game lockout season.) One more defeat will match the most losses in the Duncan Era. They are not among the top in the team defensive statistics, which so defined them in the years they either won or came close to winning a championship.

So what gives now?

“A lot of it is trust,’’ Popovich said. “You can talk about it all you want, but until you see it on the court, that’s all it is, talk. We’re starting to trust each other.”

Or, as Ginobili put it, “Our whole faces have changed.”

San Antonio’s convincing victory over the Celtics was its 11th in its last 15 games. Twelve of those games have come without the services of the ever-valuable Tony Parker, who is out with a broken bone in his right hand. The prognosis on Parker has him back in the lineup by the last week of the regular season, in time for the playoffs.

So far, the Spurs have not missed their sparkplug point guard. Ginobili is putting together a monster month filling in for Parker. He dropped 28 on the Celtics after lighting up the Cavaliers for 30 two nights earlier. In the 21 games since the All-Star break, Ginobili is averaging 21.6 points a game. Prior to the All-Star Game, he was averaging almost half that much.

“He’s basically taken over the team,” Popovich said. “He has been the same Manu we’ve had when we won championships. Without Tony, it’s really important for somebody to step up like that. He has done it.”

He has indeed. The Spurs also boast one of the league’s most productive benches – rookie DeJuan Blair is a certifiable glass eater – and, lest we forget, they also have the redoubtable Duncan. The Big Fundamental isn’t scoring the way he normally does (he’s averaging a career low 18 points game) and he has posted two dreadful shooting games in the month of March (1-of-10 and 2-of-11) which raised eyebrows around the league.

But he is averaging double figure rebounds and has been healthy for most of the season, missing only three games. And one of those was a deliberate sit-down in a back-to-back situation.

What was striking out the Spurs’ easy dispatching of the Celtics was the limited impact Duncan had on the overall game. He had 8 points, 9 rebounds and never got off the bench in the last 14-plus minutes.

“They’re doing this right now and not getting a lot out of Timmy,’’ observed Celtics coach Doc Rivers. “He still sets the table for them, because they still go to him. His numbers don’t look great. But he still facilitates the offense. They’re using him in a different way, but he’s still very effective and you still have to guard him.”

The Spurs had planned a “less is more” approach with Duncan this season, but simply could not afford that when they got off to such a slow start. Popovich still watches Duncan’s minutes with the care of a Welsh nanny and Duncan is down almost two minutes a game from last season.

“He hasn’t gotten injured. He’s had a solid steady year, no complaints,’’ Popovich said. “He’s probably been out there a little more than we normally would have liked, but we are in a position where he has wanted to play a few more minutes. And we’ve done that.”

It’s still anyone’s guess where the Spurs will end up in the Wild West. After their victory over the Celtics, they were ranked No. 6 in the conference. But only four losses – and 3 1-2 games -separated the No. 2 Mavericks from the No. 8 Trail Blazers. San Antonio has a tough final stretch; in the month of April they have eight games with five of them against the Magic, Lakers, Suns, Nuggets and Mavericks. They could wind up No. 8. Or something more San Antonio-like nearer the top.

One thing seems undeniable. They are going to be around, like always, and they could be a dangerous team when the playoffs start.

“As long as you’re playing well when the playoffs start, that’s what you want,’’ Popovich said.

Right now, he’s got exactly what he wants. Better late than not at all.