"It's an A/C joint sprain that healed on its own; I didn't have surgery," Allen, 25, said of the injury he suffered in December of his rookie year in 2013. "It happened when I dove to the ground to avoid a hit. It hasn't deterred me in any way."
Allen can't say the same for his two other football-related scars, one for surgery to repair a lacerated kidney in 2015 and one for surgery to repair a torn anterior cruciate ligament in his right knee in 2016.
The first, suffered while making a touchdown catch in Baltimore, sidelined him for the final eight games of 2015. The second, suffered before halftime of the 2016 opener, knocked him out for the rest of the season, a devastating blow for the third-round pick out of California.
But what didn’t kill Allen’s career made him stronger. After months of grueling rehabilitation and a high-intensity summer in which quarterback
He ranks fifth in the league with 1,032 yards on 77 catches entering Sunday’s game against the
Allen is the first player in NFL history to have at least 10 catches, 100 yards receiving and a receiving touchdown in three straight games.
"It didn't just happen the last three weeks," Rivers said, referring to Allen's passing the 1,000-yard mark, "but it's certainly been an awesome three weeks. He's just a guy who is so easy to feel as a quarterback.
"When I'm back there getting ready to throw it, his body language is just very inviting. When he's coming in and out of his cuts, I can just see it easily. … Some of it is reps. Some of it is just what makes him really good."
The 6-foot-2, 211-pound Allen does not have exceptional size or explosive speed, but he is an elite route runner with great hands who has benefited from the loss of seven pounds since the season opener.
"It's definitely a factor," Allen said. "I feel quicker, lighter on my feet."
The Chargers maximize Allen's agility and instincts by getting him the ball in space, using him more out of the slot, where he often draws man-to-man coverage, and throwing to him on quick slants, crossing patterns and underneath routes.
Allen, according to Pro Football Focus, ranks second in the NFL behind Detroit’s
“I watched a lot of games last year, and seeing guys like
Allen has been Rivers' go-to target in the clutch. He leads the NFL in third-down receiving with 31 catches for 464 yards.
In the third quarter of Sunday’s 19-10 win over the
Three plays later, on a third-and-goal from the seven, Allen juked right and broke left, leaving McCourty in his wake and giving Rivers a wide-open target for a touchdown and a 16-7 lead.
"He has great instincts, so he understands how to get open," Rivers said. "Just like if you're on the basketball court and a guy is guarding you, how do you get free? He knows how to separate. To me, that's what separates receivers. In one-on-one coverage, can you find a way to create separation?
"Because from back here, that separation is really what gives you the confidence that he's coming open, he's gonna be open, and when you see it over and over, it allows you to throw the ball even earlier and earlier."
Allen's understanding of the game and grasp of the playbook also have contributed to his big season.
"He knows every spot out there, not only the wide receiver group, but I bet he can tell you some of the things that are going on up front and at the running back position," Rivers said. "That takes you to a whole new level of understanding defenses, what everybody's job is and what's the point of the play."
Allen showed elite NFL receiver potential when he caught 71 passes for 1,046 yards and eight touchdowns as a rookie in 2013. But after his career was derailed by injuries in 2015, could the Chargers have expected this level of play from him?
"Absolutely," coach Anthony Lynn said. "You're talking about a high pick. That's what they do. Keenan has gotten better every single week. The guy didn't play much last year, and I think you see more chemistry between him and Phil the longer they play together."