Mesut Ozil was in, the ball on his left foot, and three points, effectively, at his mercy.

He stared down Watford goalkeeper Heurelho Gomes, “gave him the eyes,” opened up his hips, then closed them and placed a shot inside Gomes’ left-hand post. It would have been 2-0 to the Arsenal – perhaps should have been. It certainly should have been three points to the Arsenal. In the end, it was anything but.

A minute later, Richarlison baited Hector Bellerin and referee Neil Swarbrick into a penalty. A minute after that, Troy Deeney buried it. Twenty minutes later, Arsenal capitulated, and didn’t just throw away two points from a game it should have won; it threw away all three.

Tom Cleverley pounced on a rebound in stoppage time to condemn the Gunners to their first defeat since August:

Arsenal had been in control ever since kickoff, and had been in the lead ever since Per Mertersacker’s powerful first-half header.

In fact, the Gunners have mostly been in control ever since they returned from the season’s first international break. They shook off an embarrassing 4-0 defeat at Liverpool and hadn’t conceded in the league since. They had picked up 10 points from four matches, with seven goals for and zero allowed, and had vaulted themselves back up into a tie for fourth place.

On Saturday, for 70 minutes, they continued their ascent. Mertersacker’s goal was a just reward for a strong first half:

With a half-hour remaining, Ozil entered the fray, and had an immediate impact. He slid a through-ball into the path of Alex Iwobi just two minutes after his introduction. But Gomes saved a side-footed attempt from the young Nigerian.

The big chance fell to Ozil himself. Iwobi returned the favor, and the German international was free, 15 yards from goal, right above the penalty spot, with a defender trailing by some distance. His finish, though, lacked conviction, and was smothered by the Brazilian keeper.

Still, though, Arsenal seemed comfortable until Richarlison drove to the byline shortly thereafter. His touch took him inside the box, and Bellerin’s challenge was soft – soft in that it wasn’t enough to put Richarlison off, but also soft in that it shouldn’t have been enough to take the Brazilian winger down. Swarbrick, though, disagreed:

It was poor defending, but probably a poor refereeing decision too. Nonetheless, Deeney stepped up and made no mistake from the spot.

Then, in stoppage time, the ball pinged around in the Arsenal box one too many times. Deeney almost flicked it home. Cleverley smashed it into the roof of the net to send Watford up into fourth place – into the exact spot Arsenal crave, and into a spot they won’t claim if collapses like Saturday’s continue to be a regular occurrence.

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Henry Bushnell covers soccer – the U.S. national teams, the Premier League, and much, much more – for FC Yahoo and Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com or follow him on Twitter @HenryBushnell.