This is the night Matt Harvey has been waiting for his entire pitching life. The Mets, already in a world of hurt, need Harvey to rise to the challenge tonight and beat Stephen Strasburg and the Nationals. You can be sure Harvey, the young power right-hander who is making only the 14th start of his major league career, will give it his best shot at Citi Field. “He knows exactly who he is facing,’’ manager Terry Collins said yesterday in the Colorado cold as the Mets lost their third straight to the Rockies, 11-3. “He’s not one of these guys who just says, ‘I’ll take the next game.’ He knows what’s going on and who he is facing. He’s a competitor, that’s what we saw when he got called up a year ago — we saw a different animal than what we read about. And the reason is, the stage changed. “What we saw on the mound, his demeanor and everything else changed. I know he’ll be ready, because he’s facing one of the best teams in the game.’’ Since the first time I saw Harvey pitch in 2011 in the Florida State League, I’ve said he will be the rock the Mets will build on, and he has not disappointed. He is the son of a coach, a player you can lean on, and the Mets need to lean on him tonight. They are already losing sight of the Braves. But this is not about the NL East race, this is about something bigger: the Mets showing they can be a legitimate team, a team with a future. One win can point the way.