It’s not an April Fools’ joke, though watching it, I couldn’t really believe my eyes.

The Boston Celtics stunned the Golden State Warriors on Friday night, beating them 109-106 and ending the Warriors’ 54-game home win streak.

You’re probably asking right now: Wait, how did an undermanned Celtics team (they were missing Jae Crowder) beat the best basketball team in recent history? There were a lot of factors, but here were some big keys —

1. Avery Bradley made life difficult for Stephen Curry

The Celtics threw a lot of different looks at league MVP Stephen Curry — including moments with Evan Turner on him, double teams, and, at one memorable moment, having the entire team defend him.

They found their best success with Avery Bradley on him, however. Bradley hounded Curry off ball, making it difficult for him to get into his motion sets. His teammates helped him by bumping Curry off screens, and generally making his life difficult. Curry opened up in the second half — he’s the best player alive for a reason — but the Celtics were able to stay in the game because Bradley is a great defender and harried Curry for much of the first half.

2. Stephen Curry also took some time to get in the game

In the first quarter especially you could see Curry struggling with the physicality of Bradley and Turner and Marcus Smart. For much of the first quarter, he seemed content to find his teammates, or just struggled to even get the ball in his hands.

AP Photo/Marcio Jose Sanchez

Curry didn’t score a basket until the closing seconds of the first quarter. He finished with 29 and was by far the best player on the floor, but that quarter he took getting adjusted allowed the Celtics to stay in it, and find some belief.

3. Klay Thompson struggled as well

The Celtics made their plan clear — they were going to make life hard off the ball for Curry and Thompson and let the other players on the Warriors be the ones to beat them. Thompson had no baskets in the first quarter, struggling just as Curry did with the constant harassment and attention off the ball.

Unlike Curry, he never really got it going — finishing with 15 points on 6 for 16 shooting and 2 of 6 beyond the arc. Not awful numbers, but the Warriors needed a bit more from him.

4. Isaiah Thomas is a bad, bad man

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Thomas may stand just 5-foot-9, but as you watched the game you got the sense that it was turning into a straight man-off between the diminutive Celtics guard and the Warriors’ emotional center Draymond Green. Both were whooping it up after baskets, screaming at their teammates, and neither seemed willing to back down from everything.

This is funny with Thomas because, again, he’s 5-foot-9. But he refused to back down, and his ability to get past his man and repeatedly get into the paint made life extremely difficult for the Warriors. The Celtics’ offense wasn’t as pretty as the Warriors’ was by any stretch of the imagination, but again and again Thomas got into the paint and made the right decision. He finished with 22 points and six assists.

5. Marcus Smart didn’t back down from the moment

The Celtics hung tough with the Warriors in a thrilling third quarter that saw Stephen Curry turn into a human fireball, and somehow the Celtics returning every punch. To kick off the fourth quarter, the Celtics landed a surprising blow when Marcus Smart got a few mismatches on Mareese Speights and didn’t hesitate. On the first he attacked the basket and laid in a wonky runner.

He followed that up with a three-pointer in the big man’s face.

The two buckets grew the Celtics’ lead, and you could see the team really starting to believe.

6. Evan Turner had one of his best games ever

AP Photo/Marcio Jose Sanchez

Turner is a player who is not quite what most modern NBA teams are looking for. He can’t really shoot the three. He loves a good mid-range jumper, the inefficient shot that is that antithesis of all that is NBA gospel right now. And yet that weird mid-range game he loves so well was devastating for the Warriors. The Celtics kept working the ball around, forcing switches until Turner had someone he felt comfortable posting up. He finished 8-13 from the field for 21 points, and tacked on 5 assists and 5 rebounds.

7. The Celtics turned the game into a mud fight

Ezra Shaw/Getty Images

The Warriors’ offense is one of the most beautiful things in sports, but there is a way to disrupt it — you turn the game ugly. The Celtics did that. They hung guys up on screens, dove after loose balls, banged bodies in the post.

As soon as the game got the feeling of that playoff atmosphere, the refs more or less put the whistles away … just what the Celtics wanted.

8. Brad Stevens is an incredible coach

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This is the long and the short of it — Brad Stevens had a perfect game plan and the Celtics executed it perfectly.

They hounded the Warriors off the ball, refusing to let them get into their sets. They took the shots the Warriors gave them, even if they weren’t pretty. The Celtics moved the ball exceptionally well and found the right pass time and time again.

He took this starting lineup …

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… and beat the defending champions on their court. That is stunning.

He did it by taking advantage of all the things listed above, but also by instilling in the Celtics a sense of belief that they belonged on the floor with this team and that they deserved to win the game.

Now, for the huge caveat —

The Warriors are still the best team in the NBA. The Celtics played a near-perfect game and were a rimmed-out Stephen Curry three from having that game go to overtime. The Warriors were missing Festus Ezili and Andre Iguodala. If the Celtics somehow claw their way out of the Eastern Conference and meet the Warriors in the NBA Finals, the Warriors probably win in five.

But the Celtics did show that there is a way to beat this Warriors team. You have to be willing to get ugly, to take mid-range shots, and to work your tail off on defense. And you need a little luck.

Actually, yeah, that’s number 9 on this list.

9. The Celtics got a bit lucky

The Warriors uncharacteristically turned the ball over a few times down the stretch. They don’t usually do that. The Celtics hit some weird floaters and got a few non-calls and had bouncing balls break their way.

But for a team like the Celtics to stun the Warriors in Oakland, they needed a little luck. Any team does. That shouldn’t take away from what they accomplished.

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