When the season began, the conventional wisdom on the Houston Rockets was that they were a good team (a rung below the elite) — and that stature depended on the team’s superstars, center Yao Ming and swingman Tracy McGrady, staying healthy.

But as we approach the halfway mark, that thinking needs some revision. True to their track record, the Rockets’ stars have missed time. McGrady has sat out seven of Houston’s 38 games with back ailments that have nearly derailed his stellar career. Ming has missed the last 11 with a knee injury and is not expected back until mid-February. When Houston was forced last season to play large chunks of the campaign without its superstars, whose combined absences totaled 60 starts, it plummeted to a 34–48 record, just one season after going 51–31 and taking Dallas to a seventh game in their opening round series. Now, the Rockets are 25–13, the fourthbest record in the league, and they’ve won nine of 11 since Ming’s injury.

This alone should get their coach, the curmudgeonly former Knick, Jeff Van Gundy, to crack a smile every now and then, but there’s more. The Rockets sport a point differential — an excellent predictor of future performance — far better than their lofty winning percentage. Their average victory margin of six points a game puts them on pace for a 60-win season. (By contrast, the differentials of the Jazz and the Lakers suggest struggles ahead). These kinds of numbers matter to Rockets assistant general manager Daryl Morey, who will take over as team president when current general manager Carroll Dawson retires after the season. Morey built his reputation on statistical analysis rather than scouting, and has sought to bring in more efficient players to support T-Mac and Yao this season. It’s been whispered that his impending takeover in the front office would put VG on thin ice. Yet, this is a Van Gundy team through and through. Houston plays at a snail’s pace: Their 88.8 possessions per game is the fifthslowest in the league, and the team ranks first in Defensive Efficiency (points allowed per 100 possessions) at 99.6. If all this doesn’t make Van Gundy’s lips tick upward from time to time, then we can assume the agony of those millennial-era Knicks teams have ruined him for life.

For most, the Rockets’ midweek tussles with Dallas and Phoenix will serve as the litmus test for their place among the elite. But Houston’s credentials are already in tact. Before anyone outside South Texas took notice, the Rockets thumped Dallas by 31 and San Antonio by 19. The victory over the Spurs at the AT&T Center was significant because the Rockets were still without McGrady, while the Spurs’ rotation was undisturbed.

Overall, the Rockets have gone from eighth in Defensive Efficiency to first and they’ve enjoyed an even bigger boost on offense. Last season, the team ranked 29th in Offensive Efficiency — for a plodding team, this had to be absolute drudgery for fans — but this season they’ve vaulted to the middle of the pack at 15th.

Aside from a draft day deal that brought Shane Battier to Houston in exchange for Stromile Swift, the personnel changes among the Rockets’ supporting cast have been minimal. Instead, change has come in the form of holdovers. Guard Luther Head is playing more minutes and has been somewhat more effective, and forwards Chuck Hayes and Juwan Howard have been productive in limited roles. The big boost has come from backup center Dikembe Mutombo, who is 40 — or at least that’s the story he’s sticking to. He is playing like a much younger man; since January 1, he’s averaging 15.3 boards per game and his stellar play has helped the Rockets weather Yao’s absence.

The other key factor is T-Mac’s return to form. His back limited his playing time during the last two seasons, and the ailments further diminished his effectiveness. After visiting a specialist in Waco, Tex., McGrady has been playing like he did when he was a perennial MVP candidate. This month, he’s averaging 27.7 points, 7.6 assists, and five rebounds per game. He’s referred teammate and fellow back- pain sufferer Bonzi Wells to the same doctor. If Wells suddenly improves this summer, the line from Waco may stretch all the way to Dallas for this doctor’s services.

T-Mac has played at this level before, so it’s not unreasonable to assume that his improvement is sustainable. Mutombo is playing nearly twice as many minutes per game as he did last season, and that may need monitoring to ensure he doesn’t run out of gas before Ming’s return.

But when Ming rejoins the Houston lineup after All Star Break, the Rockets may vie for a homecourt advantage in the second round of the playoffs. The Rockets’ improved play looks to be the real thing. Barring another TMac injury, it seems that the NBA’s big three just became a big four.

mjohnson@nysun.com