David Robinson is a Navy man. You’d think he pretty much stays on an even keel.

But Robinson can’t help jumping out of his seat these days at the AT&T Center. The Hall of Fame center hardly can believe the success of his former team.

“Absolutely, I’m surprised,’’ Robinson said of the gaudy 50-11 record of the San Antonio Spurs. “I expected them to be good but the record they have put up is ridiculous. It’s ridiculous. (It’s) unbelievable.’’

The Spurs became the first NBA team this season to reach 50 wins with a 109-99 triumph Wednesday at Cleveland. They’re on pace to go 67-15, which would be the best record in team history and a win total only nine NBA teams have reached.

The Spurs have won 60 or more games three times before. They put up 62 in 1994-95, when Robinson was MVP, 60 in 2002-03, Robinson’s final season, and won a franchise-record 63 in 2005-06, when big man Tim Duncan was in his prime.

But nobody anticipated what would happen this season. The Spurs were coming off a 50-32 mark in 2009-10, their worst in 13 years. They were looking old and injured.

Some thought the Spurs, who won titles in 1999, 2003, 2005 and 2007 under coach Gregg Popovich, might blow it up and look more toward the long-term future. But no dynamite was carted into the Alamo City.

After he opted out of his contract, the Spurs re-signed underachieving forward Richard Jefferson to a four-year, $39 million deal. Jefferson’s scoring average is actually down from last season, from 12.3 to 11.6. But he’s been much more of an outside threat, raising his three-point percentage from 31.6 to 43.6 and closing in on having made twice as many three-pointers as last season.

The Spurs resisted the urge to trade point guard Tony Parker, who showed some signs of slippage during an injury-riddled 2009-10. Instead, they signed Parker to a four-year, $50 million contract extension at the start of the season. Parker, 28, has bounced back strong, although he was lost earlier this week for two to four weeks due to a calf injury.

The Spurs also didn’t worry when looking at the calendar and seeing Duncan will be 35 in April. Popovich simply devised a plan of further cutting his minutes to keep him fresh. Duncan, who in his heyday played 40 minutes a night, is averaging a career-low 28.8.

Still, it looked as if the Spurs’ best hope was to squeeze out another 50-something win season and then try to turn it on the playoffs. But being on pace now to reach the upper 60s in wins? No chance, right?

“I’m surprised, actually,’’ said New York forward Amare Stoudemire, who had lost four consecutive playoff series to the Spurs while with Phoenix until the Suns swept San Antonio 4-0 in a Western Conference semifinal last spring some thought might have been a sayonara series for the Spurs. “I didn’t think they would be this good. But I knew they were going to come back because they have their core guys and the guys who have been there forever.’’

That category includes Duncan, Parker and guard Manu Ginobili, who all have been around at least nine years in San Antonio. Then there’s Popovich, who is in his 15th Spurs season and has the longest ongoing tenure of any NBA coach after Jerry Sloan resigned from Utah last month.

But even Popovich didn’t see this coming.

“I think everybody is surprised the record is what it is,’’ Popovich said when told about Robinson being flabbergasted. “There’s no reason why David shouldn’t be surprised too. I’m surprised. You don’t go into (the season) saying by the All-Star break we want to have 46 wins (the Spurs were then 46-10). That doesn’t happen that often.’’

It sure doesn’t. During San Antonio’s title seasons of 2003, 2005 and 2007, they had records at the break of 33-16, 41-12 and 35-18, respectively (there was no All-Star game during the 50-game lockout season when the Spurs won their first title in 1998-99).

With the exception of the 2005 championship team, which started 47-13 before finishing the regular season a mundane 12-8, San Antonio title teams usually have started slow and then shifted into gear at the end. The 1998-99 outfit began 6-8, the 2002-03 team 12-9 and the 2006-07 gang was 33-18 before going on an incredible 25-3 spurt.

It’s interesting to note the team that provided Popovich with the best regular-season record in team history didn’t even make it to the conference final. The 2005-06 Spurs were ousted 4-3 in a West semifinal by Dallas.

Considering San Antonio’s trademark is usually playing its best ball at the end of the season rather than at the start, Popovich does admit some concern about his team peaking too early.

“Absolutely’’ he said. “I hope this doesn’t mean that we can’t do what we usually do in March and April and get on a good run, that it exempts us from that. So we’ll see.’’

The Spurs could face some adversity due to Parker’s injury. But you get a feeling that San Antonio, called the “smartest team in basketball’’ by Denver coach George Karl, will figure it out.

The Spurs are 2-1 without Parker, including last Sunday’s 95-88 win over Memphis, when he was done for the night in the second quarter. That was their 21st straight home win, which tied a single-season team record and which they will try to break when they play host to Miami on Friday in a possible Finals preview.

Filling in for Parker has been George Hill, who had 22 points against the Cavaliers. Hill emerged last season as a second-year man and this season’s big surprise has been guard Gary Neal, whose minutes are becoming even more important with Parker out. Neal ranks sixth among NBA rookies in scoring with a 9.3 average despite having hardly taken the traditional route by being undrafted in 2007 and playing three years in Europe.

Throw in San Antonio’s terrific trio of Ginobili, averaging a team-high 18.0 points, Parker, averaging 17.1, and Duncan, still putting up 13.5 points and 9.5 boards a night, and the wins have been piling up.

“You can’t anticipate the chemistry thing,’’ Robinson said. “And I think the chemistry factor, with the young guys coming in (Hill, Neal and second-year big man DeJuan Blair), and you’ve just got the right mix of guys and a great level of confidence. They’ve proven to me, day in and day out watching them play, that they can do this all year long. This is not some kind of a little run that they’re going through. They’ve dominated night in and night out.’’

In other words, Robinson expects the ridiculousness to continue.