Pau Gasol (left) hasn’t been a hand-in-glove replacement for the retired Tim Duncan. (Rich Pedroncelli/AP Photo)

SACRAMENTO – For the past 19 years, the San Antonio Spurs have been defined by the stoic presence of Tim Duncan. As one of the best players in the history of the sport, a two-way monster who could have a profound impact on any play at any time, he became the foundation for everything Spurs Coach Gregg Popovich has built in San Antonio as the Spurs have become one of the model franchises in all of sports.

That’s what makes things so strange for the Spurs this season, as they have begun the six-month odyssey of the NBA regular season for the first time in nearly two decades without the player synonymous with the team’s success.

“It’s going to take some time, that’s for sure,” Tony Parker said with a smile after the Spurs beat the Sacramento Kings, 110-105, inside the Golden 1 Center Wednesday night, “because Timmy covered a lot of stuff for everybody.”

Duncan remained a hugely important part of the Spurs right up until he removed his uniform for the final time after scoring 19 points in 34 minutes in San Antonio’s 113-99 loss to the Oklahoma City Thunder in Game 6 of the second round Western Conference playoff series.

That was particularly true on the defensive end, where even in his 19th and final season Duncan remained one of the elite defensive players in the sport. San Antonio’s defense was the best in the NBA last season, allowing 96.6 points per 100 possessions to their opponents, according to the league’s metrics. When Duncan was on the court? That number dropped to an absolutely absurd 93.8 points per 100 possessions – a full point better than the NBA’s Defensive Player of the Year last season, teammate Kawhi Leonard.

While that’s only one statistic, it is a legitimate barometer for Duncan’s ability – even as his offensive touch often eluded him in his final season, and knee issues at times limited his mobility – to still be an imposing backline for the Spurs’ defense. He directed traffic and provided a kind of familiar security blanket that Parker and the other Spurs knew would always be in the right place at the right time.

“You have a great deal of corporate knowledge when you play together for so long,” Kings Coach Dave Joerger said. “You feel each other. Guards are out there and not knowing where screens are coming from, and that relationship goes on for years and years, and really does help in especially pick-and-roll coverages.

“They had a nice chemistry where he knew what he could do and where they could send them and help Parker a little bit, and it just takes time [to adjust].”

And that’s where the decision the Spurs made to replace Duncan with another aging Hall of Fame big man, Pau Gasol, becomes a truly fascinating one. Gasol has had a stellar career of his own, as between his time with the Memphis Grizzlies, Los Angeles Lakers and Chicago Bulls he has become one of the best international players in the history of the sport. Having earned a pair of championship rings with the Lakers, a pair of silver medals and a bronze in three Olympic Games and a gold at the 2006 World Championships, Gasol’s place in the history of the sport is more than secure, and he showed he can still play Wednesday by putting up 24 points, nine rebounds, two assists, two blocks and no turnovers against the Kings and their All-Star center, DeMarcus Cousins.

But while Gasol plays the same position as Duncan, they do so in entirely different ways. While Duncan’s strengths were on the defensive end in his later years, Gasol remained effective because of his offensive gifts. He’s still an excellent passer, as well as someone who can score both in the low post and out on the perimeter with an effective mid-range jumper. But while Gasol is long, and thus able to block some shots, he’s never been known as anything like the kind of defensive stopper Duncan was – which puts him in the awkward position of having to try to fit into a new team in the role of someone who played it far differently than he will.

“I didn’t come here to replace Tim,” Gasol said. “Tim is an incredible player, a player that I looked up to, an icon in San Antonio, and anywhere else, for that matter. But I just came to bring my talent, my abilities and help this team be the best it can be. That’s what I’m focused on. I’m not going to try to be someone that’s played here 19 years, got five championships with this team. I’m trying to help this team get one, and that’s where I’m at.”

If the Spurs are going to be a true championship contender, however, they’re going to need to figure out a way to defend with Gasol and Parker on the floor. So far, the numbers say that’ll be a difficult task.

Although it’s undoubtedly a small sample size – Gasol has played in all 12 games, but Parker has already missed four with a sore right knee – so far the Spurs are significantly worse when both of them are on the court defensively. When Gasol is on the court, the Spurs are allowing 104.6 points per 100 possessions, compared to 96.8 when he’s on the bench, while for Parker the marks are 105.5 and 98.2, respectively.

While the overall numbers for the Spurs are as healthy as ever – the team currently sits eighth in the league with an average of 100.7 points per 100 possessions allowed through Wednesday’s action – finding a way to cover up for their lack of athleticism at both point guard and center in their starting lineup because of their aging stars at both positions will be a critical problem to solve between now and the playoffs.

“[With] the way the NBA is going, there’s so much switching going on, and smaller lineups, so it is an adjustment period that just continues to happen that way,” Gasol said. “We’ll continue to help each other out, understanding how we can help each other on the floor and communicating. That’s the key no matter what.

“I’ll do as good a job as I can, and that’s what I can do.”

After losing three out of four games to start November, Wednesday’s win over Sacramento was San Antonio’s fourth straight, and at 9-3 with a bonafide MVP candidate on the roster in Leonard, it looks like the Spurs are going to rattle off another 55 or more wins this season as they have for so many years with Duncan leading the way. Only now they have to try and figure out how to make up for his loss without a replacement who can do the same things he did.

“Pau is doing a good job so far,” Parker said. “I always say you can’t replace Timmy, but you just have to do it differently.”

For Gasol and the Spurs, that isn’t just friendly advice: it’s an acceptance of the reality of their situation.