There have been times during the past week when Spurs forward Boris Diaw has looked at his oldest teammate and had to do a double-take.

The way Tim Duncan has played of late, it’s as if all the gray has gone from his beard, the youthful spring has returned to his step, and he is 28 years old instead of 38.

“Sometimes sitting on the bench you look up and say, 'Look it’s young Timmy,’” Diaw said.

The coach who has known Duncan the longest isn’t fooled.

To truly appreciate what Duncan is accomplishing in his 18th NBA season, Gregg Popovich suggests you watch the Spurs’ captain walk to his car after a game.

“I mean if you watch him walk, he limps,” Popovich said. “His leg doesn’t extend. So it’s, 'How does this guy play?’”

Indeed, Duncan’s left knee — encased in a bulky black brace each game night — has been ravaged by the pounding of 52,172 NBA minutes (including postseason).

That knee, perpetually crooked at a slight angle, tells the truth. Young Timmy isn’t so young after all.

More Information By the numbers Tim Duncan’s stats so far this season solidly put him into the All-Star Game conversation once again (figures per 100 team possessions): 1.6 steal percentage, best of career 5.3 block percentage, tied for third best of career 19.5 total rebound percentage, second best of career 22.8 Player Efficiency Rating, slightly better than rookie year (22.6) 45.1 opposing FG percentage at rim, eighth among defenders facing at least six attempts per game 96.7 defensive rating, fourth in NBA This season: 17.9 points, 12.4 rebounds, 3.4 assists, 2.5 blocks, 1.1 steals Career: 20.5 points, 11.5 rebounds, 3.2 assists, 2.3 blocks, 0.8 steals E-N research: Dan McCarney

Read More

And yet, here is Duncan at 38, the Fundamental in winter, averaging 16 points, 11 rebounds and 2.3 blocks with efficiency numbers that rival his MVP heyday.

The genius of Duncan is not his refusal to age, but his insistence at aging gracefully.

It has been years since Duncan has been the centerpiece of the Spurs’ offense. Instead, he has channeled his twilight-years energy into rebounding and shot-blocking, and ranks in the NBA’s top 10 in both categories.

“Got to change with the times,” said Duncan, who is averaging 25.3 points, 12.7 rebounds and 2.3 blocks in his past three games. “I can’t jump and move like I used to, so I have to adjust and get into position and anticipate and do whatever I can to get there early.”

Unlike other declining superstars who choose to spend their later seasons stubbornly clinging to a style that no longer works for them (see Bryant, Kobe), Duncan has altered his game to maximize what he has left.

He will never be the basketball equivalent of the old guy at the club, trying to beat teenagers at their own game.

Instead, Duncan does what he can still do, in some cases better than he used to do it. The two-time league MVP has, in a sense, moved his wheelhouse.

Duncan’s 12.4 rebounds per 36 minutes are the most of his career. His 2.5 blocks per 36 minutes are higher than his career average.

According to ESPN’s formula, Duncan leads the NBA in real defensive plus-minus, an advanced statistic that measures a player’s defensive impact when on the floor.

If Duncan continues at this pace until February, he stands a good chance of becoming only the fourth player in NBA history to make an All-Star team after his 38th birthday.

“He’s doing it differently,” Popovich said. “Now he does his work early all the time. He puts his body where it needs to be because he can’t make up for it with his athleticism. His timing is even better than it used to be.”

One example of Duncan’s mastery of the NBA chess game came late in Monday’s 125-118 victory over the Clippers.

Blake Griffin, the Kia-jumping, pogo-legged forward, was driving toward him. DeAndre Jordan, the high-flying center, was cutting behind him.

Sensing Griffin was setting up for a lob to Jordan — an automatic two points — Duncan timed the pass perfectly, tipping the ball away without leaving the ground.

“He’s a sensational player,” Clippers coach Doc Rivers said, “with a mind to match.”

Rivers was a television analyst covering the Spurs early in Duncan’s career. In 2000, after Rivers got the job coaching Orlando, he tried to recruit Duncan to the Magic.

Rivers acknowledges the Duncan he sees now is different than the version he saw then.

“The older players are searching, because they know they are losing a step,” Rivers said. “I saw Kevin (Garnett) going through the same thing. They are in a constant search to figure out the right way to adjust.

“Tim has clearly found whatever that is.”

Then there are the moments when Young Timmy comes back.

In two grueling triple-overtime games last week, Duncan went — in Popovich’s words — “Back to the Future.”

On Wednesday, Duncan scored 23 points with 16 rebounds and three blocks in 43 minutes against Memphis.

Two days later against Portland, he was even better — a season-high 32 points, 10 rebounds, and four blocks in 48 minutes.

Showing little inkling of exhaustion, Duncan was still swatting shots in his sixth OT period of the week.

The Spurs lost both games, squandering vintage performances from Young Timmy.

“It really hurts when Timmy does what he’s been doing and we lose,” Popovich said. “It’s like you wasted him for a game.”

Someday soon there will be no Duncan left to waste.

Young Timmy will become Retired Timmy, and when that day comes, Duncan will walk away from his Hall of Fame career in the same manner in which he finished it.

With a slight limp that belies his lasting place in the game.

jmcdonald@express-news.net

Twitter: @JMcDonald_SAEN