The Miami Heat did what everybody expected: they came into the gym of the favored but younger Philadelphia 76ers, and punched them in the mouth. Miami rudely hung 35 points on their hosts in the opening quarter and 60 by halftime, drilling 3-pointers and moving bodies and ball, working overtime to slice up a defense that finished the regular season ranked third in the NBA in points allowed per possession.

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But the regular season ended Wednesday, and for Brett Brown’s largely inexperienced Sixers, Saturday evening represented a whole new ballgame. The sixth-seeded Heat brought the heavy artillery to start out, demanding the higher-seeded hosts prove they could respond in kind before they’d believe in the bright young things in the white and blue uniforms.

So the Sixers did after halftime what they’ve been doing for the past three months. They proved that they are for freaking real.

Even without injured All-Star center Joel Embiid, who’s still working his way back from a fractured orbital bone and whose contributions were limited to a pre-game bell-ringing ceremony as the “Phantom of the Process,” the Sixers absolutely dominated the Heat in the second half. Philly clamped down defensively in the third quarter and ran Miami off the court with 3-point shooting and cuts to the basket on their way to a convincing 130-103 win in Game 1 of their first-round series on Saturday.

The Sixers’ much-lauded youth was most definitely served at Wells Fargo Center. Rookie of the Year favorite Ben Simmons opened his postseason career with a brilliant 17 points, 14 assists, nine rebounds and two steals, while fellow playoff debutantes Robert Covington (nine points, seven rebounds, four assists, three blocks, tremendous individual and help defense), Dario Saric (20 points, six rebounds, three assists) and Markelle Fultz (five points, four assists, two steals, two rebounds off the bench) all contributed to the victory. But it was several Sixers veterans who set the tone and put Philly on the path to a 1-0 lead in the best-of-seven set.

Shooting guard J.J. Redick, the calm and experienced sniper the Sixers paid $23 million on a one-year deal to settle and organize a young crew, earned his money on Saturday, coming alive in the second half to score 28 points (8-for-13 shooting, 4-for-6 from 3-point range, 8-for-8 from the foul line) in the win. Reserves Marco Belinelli and Ersan Ilyasova, both of whom started the season with the Atlanta Hawks, provided exactly the offensive spark that general manager Bryan Colangelo had hoped for when he scooped them up on the buyout market late in the campaign. The veteran shooters combined for 42 points on 32 shots — including seven of Philly’s 18 3-pointers — to help kickstart an offensive explosion after halftime that overwhelmed the Heat, leaving them wondering what had hit them, licking their wounds and trying to regroup in hopes of salvaging a split on the road in Game 2 on Monday.

After watching the Heat get many of the kinds of looks they wanted in the first half without making necessary defensive tradeoffs, Brown — a longtime Gregg Popovich acolyte in his first playoff game as a head coach after four years of wading through muck and rebuilding mire in the City of Brotherly Love — opened the third quarter by shuffling his starting lineup. He put stalwart defender Amir Johnson on the bench and sent floor-spacer Ilyasova in as a stretch five, forcing Heat head coach Erik Spoelstra to make a big decision. Would Miami keep center Hassan Whiteside on the floor, aiming to bust the small-ball Sixers up inside? Or would Philly be able to play the Heat’s behemoth big man off the floor, forcing Spoelstra to downshift and perhaps tilting the matchups in the Sixers’ favor?

The Sixers’ shuffled-up five-out offense immediately paid dividends, creating cleaner openings for cuts and passes. When Miami couldn’t capitalize on the size mismatch on the other end, Philly had found a formula for tilting the game, opening the third quarter on a 13-3 run to regain the lead and, with 7:54 left in the quarter, forcing Spoelstra to pull the trigger and sit down his high-priced big man … which didn’t seem to sit all that well:

Despite Spoelstra turning back to reserve center Kelly Olynyk, who’d played wonderfully in the first half and finished with a Heat-high 26 points on 9-for-13 shooting to go with seven rebounds and two assists in 31 minutes off the bench, Miami just couldn’t get unstuck in the third. The Heat stayed icy, missing 10 of their first 11 shots of the second half and finishing 5-for-19 in the quarter as they let the Sixers build momentum behind absolutely beautiful defensive work. Philadelphia’s phalanx of well-drilled, long-armed defenders switched assignments on the perimeter before recovering to shooters, tagging rollers, getting their hands in passing lanes, making second efforts to contest shots on back-door cuts and late passes, and generally wreaking havoc on a Miami team that relies more on collective execution than individual shot creation to generate quality looks.

The Sixers ripped off a 20-2 run, changing the terms of engagement, and finished off a 34-18 third quarter that seemed to completely dispirit the visitors. Miami never again got the margin into single digits. Redick poured in 15 points in the final frame to keep the Heat at bay, and Saric and Belinelli combined for 15 more, as Philly closed the door with a 40-point final frame that emphatically drove the point home. Yeah, the 76ers are young, and yeah, this is their first postseason rodeo, but they are here, and they’re absolutely prepared to whip the hell out of anybody who steps on the floor against them.

This was the Sixers’ 17th straight win dating back to March 15, and like many of the preceding 16, it seemed downright matter-of-fact. This isn’t your average team of first-time performers. They’re serious as a heart attack and real as it gets, and it’s up to Spoelstra and company to figure out how to shake them up before Game 2 tips off on Monday night. Because, as it turns out, just coming into their arena and throwing a haymaker ain’t enough. These Sixers are tough enough to take it on the chin and return fire in kind until you’re looking up at the lights, wondering what the heck just happened.

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Dan Devine is a writer and editor for Yahoo Sports. Have a tip? Email him at devine@oath.com or follow him on Twitter!

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