The Chargers led 20-17 in the fourth quarter and had forced the Chiefs into a precarious third-and-20 with about a minute to go. When the reigning Super Bowl MVP dropped back to pass, trying desperately to get his team into position for a field goal to force overtime, the Chargers had the Chiefs' fleet of speedy wide receivers blanketed downfield.
Then they watched in horror as Mahomes slipped through a crack and dashed 21 yards for a first down.
For all the publicity Mahomes gets for his strong arm - the one capable of throwing a football over the upper deck and out of Arrowhead Stadium - what often gets overlooked are his legs. He may not be predecessor Alex Smith or Ravens signal caller Lamar Jackson, whom the Chiefs face Monday night, but Mahomes is dangerous enough to keep defenses honest.
The Chargers were reminded of it. That scramble for a first down allowed the Chiefs to get into range for Harrison Butker to kick the tying field goal. Then in overtime, Mahomes scrambled again on third down to help set up the winning 58-yarder.
''That's always been part of this offense,'' said Chiefs coach Andy Reid, who proceeded to rattle off names of those who have flourished in the modified West Coast system that he learned from Bill Walsh and Mike Holmgren.
Joe Montana and Brett Favre could scramble. Steve Young and Donovan McNabb could run. Michael Vick may still be the fastest and most athletic quarterback ever to play in the NFL.
''They're all mobile guys and they can get out and go when needed,'' Reid said. ''You don't want to make a living on it. But the one unique thing is all the guys keep their eyes downfield. All the great ones. So they're still putting pressure on the defense with the opportunity to throw the football. I think that would be universal.''
To be sure, the ability of Mahomes to fling the ball downfield at any moment makes things easier on the ground. At one point against the Chargers, he was scrambling to his right and still had the arm strength to throw an off-balance strike to Tyreek Hill more than 50 yards downfield for a diving touchdown reception.
Defenses have to blanket Hill and the rest of the Chiefs' wide receivers until they know Mahomes is going to run. And by that point, it is often too late to prevent him gaining at least a handful of yards and usually a first down.
''The good things about the guys on my team, and the receivers and tight ends, defenses have to be accountable for those guys,'' Mahomes said. ''They're getting deep (so) they're trying to stop them from going over the top. So when there's room to run, I have to take advantage of it. Defenses aren't leaving their guys, so I have to be able to run.''
Perhaps it was apropos that on a Zoom call this week in which Mahomes discussed his scrambling ability, who should pop up on the screen but Vick himself. Now an analyst on the FOX pregame show, the four-time Pro Bowler set the NFL record for rushing yards by a quarterback during a career that ended under Reid in Philadelphia.
''I don't know if I can run like Mike,'' Mahomes said with a wry smile, ''but I can get a few yards and get out of bounds.''
Mahomes doesn't necessarily look fast; his body type is a bit stocky. But he grew up playing all sports, and was a standout on the baseball field and basketball court. That athletic background has made him deceptively quick when he tucks the ball and runs. Linebackers and defensive backs alike often have a hard time trying to track him down.
Mahomes is also smart enough to know his value, which is why he is almost never tackled. The vast majority of his runs end up with Mahomes sliding before he takes a hit or effortlessly waltzing out of bounds.
''When it's third-and-long, or third-and-short, he can take to his feet and get the first down,'' said Chargers quarterback Justin Herbert, who probably learned a few things watching from the sideline during his first NFL start. ''Those are the plays that you cover as many guys as you can and a guy like that has the legs to run - it's really tough defending him.''
The San Francisco 49ers learned that in the Super Bowl. Mahomes ran nine times for 29 yards and a touchdown, helping the Chiefs end a 50-year championship drought with a stirring come-from-behind victory in Miami.
''With Mahomes, as good as he is in the pocket, he's just as good - probably better - outside the pocket, which is the craziest thing about his game,'' Ravens cornerback Marlon Humphrey said. ''Preparing for him, it's really tough. You can't say any team has really just been able to stop him completely. He's never really out of a game.''
Thanks to his legs, he's never really out of a play, either.
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