HOUSTON — Power, above all else, defined Matt Harvey. It once was at the center of his identity as a pitcher. It’s what allowed him to attack the strike zone with no fear, to move batters off the plate, to morph into an unrelenting bully.

“What made him exceptional is that he could throw it 96, 97 mph,” said Mets manager Terry Collins, who once wagered an entire franchise’s World Series ambitions on the potency of that power.

But 2015 was a long time ago, and that version of Harvey has been replaced by the one that will appear here on Saturday afternoon when the Mets open a doubleheader against the Astros. Power no longer is a given, though uncertainty still is.

“If I can keep the mechanics the way I want to, velocity will be there,” Harvey said earlier this week.

The righthander sought to dismiss concerns about the missing velocity on his fastball, but the trend has been clear. His most defining weapon has diminished as his body has shown more signs of wear every season, falling from an average high of 97 mph during the pre-Tommy John heights of his career in 2013 down to 94.6 mph this season. That was before a stress injury in his shoulder sent him to the disabled list in June.

During that 11-week recovery, Harvey worked to strengthen the area behind his right shoulder, which had atrophied in the aftermath of surgery last season to correct thoracic outlet syndrome. But his minor-league rehab assignments raised red flags, thanks to mediocre results combined with a fastball that hovered in the range of 92 to 93 mph.

“I think everybody’s so worried about velocity,” Harvey said. ”It’s about getting hitters out, that’s the biggest thing. If I can go out there and be healthy and get people out, that’s the most important thing.”

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But since the 2015 World Series, Harvey has shown no ability to get people out with any semblance of consistency. In the last two seasons, he has logged 163 innings over 30 starts with an 8-13 record, a 5.02 ERA and a 1.46 WHIP, a shell of his former self.

“It’s been two years of having some troubles in between starts, trying to figure out why innings were so bad, why I couldn’t stay healthy or [not] sore between starts,” Harvey said. “Bullpens were becoming a task and that’s not usually how things go or should go. Trying to fight through that was not easy.”

Things are different now, Harvey insists. With rest, he has been able to sidestep the pain that plagued him between starts.

“It’s been a relief to come back after two months off and be able to throw in between starts, get my work done, have no pain and have no issues, and feel like we’re going in the complete opposite direction,” he said. “The right direction.”

As for velocity, he explained the dip during his rehab starts to focusing on mechanics and pitching without the adrenaline rush of a big-league crowd. It’s a common complaint for those coming back from an injury.

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Now Harvey returns to the spotlight. In a strange coincidence, he’ll pitch in the first sporting event here since Hurricane Harvey brought devastation upon a region that is in the infancy of its own recovery.

“Being healthy is the biggest part, finally coming back and not having any issues in between an outing or like a bullpen session, not getting sore from those, that’s the biggest thing,” Harvey said. “If I can get five or six solid starts in and feel healthy and strong between each start and going into each start, going into the offseason strong and healthy, that’s the biggest thing.”

For Harvey, 28, the next month is the beginning of a crossroads. After next season, he is a free agent. And although other teams hoped to buy low in a trade for him, the Mets did not entertain any of that talk. Instead, the Mets enter 2018 hoping that the motivation of a walk year can spur Harvey.

First, they must learn what they have in him and what they don’t. And if the velocity is slow to return, the first step in that process might be determining what a power pitcher can do when deprived of power.

“If he pitches at 93, 94,” Collins said, “still that’s very, very good.”