He led the league in receiving yards (1,535) and receptions (127), and led his team in receiving touchdowns (eight). However, that last category nearly belonged to then rookie Gabriel Davis, who had a friendly wager with Diggs on who would catch the most touchdown passes in 2020.
Davis (35 catches on 62 targets) finished with seven receiving touchdowns, but had a pair nullified by Buffalo penalties -- an illegal shift (against the Tennessee Titans in Week 5) and an illegal formation (against the New York Jets in Week 7). The 2020 fourth-round pick proved to be quite a find and impressed Diggs.
"I try not to put too much pressure on the young guys," Diggs said of Davis. "He handled himself extremely well as a professional. He had success and he handled success well ... He's a humble kid, he's a kid that works extremely hard, and I look forward to him taking that next step."
Davis (6-foot-2 and 210 pounds) was a standout during training camp last season and played a larger-than-expected role when starter John Brown was forced to miss seven games with various injuries. Davis shined during the Bills' final eight games, when he had five of his TD receptions.
His ability to play any receiver spot contributed to rookie success.
"I've been playing a role of just being available," Davis said last season. "Being ready to play every single position, know what everybody's doing and be able to fill in for the spot. [Brown] went down and I just had to be ready. I've been practicing every single day for an opportunity like this."
Davis seemed like the favorite to fully replace Brown, who was released by the Bills in March, but his path to a starting job became more uncertain when Buffalo signed veteran Emmanuel Sanders (61 catches with the New Orleans Saints) during NFL free agency. Cole Beasley (82 catches) also commands a lot of attention from quarterback Josh Allen.
As Diggs put it, playing in such a deep receiver room could be tough for younger players because "there's only so many balls that can go around," but it hasn't been a problem for Davis. In fact, his coaches say he's used the opportunity to learn from the players above him, rather than worry about getting his share of the targets.
Bills offensive coordinator Brian Daboll said the influence Diggs, Sanders and Beasley have had on Davis has been invaluable.
"The receiver position is a tough position to play coming out of college. He was a productive player for us last year with all that we asked him to do," Daboll said. "He has all the traits that you look for -- he's smart, he's tough, he's big and he's got, I'd say, game speed. Maybe it's not a 4.3[-second] 40[-yard dash], but when he's running out there, he can run by guys.
"It's really helpful for him to watch guys like Stef and Bease and Sanders, watch their body language and how they get in and out of breaks. He does a really good job of watching the guys ahead of him and then can emulate it."
Davis showed signs he could handle any assignment at the 2020 scouting combine, where he impressed the Bills' front office with his maturity. Daboll said Davis left them with the impression he understood football and could succeed in a system that "puts a lot on" its wide receivers.
After leading NFL rookies by averaging 17.1 yards per catch during his 599-yard season, the Central Florida product has continued to impress throughout spring practices and the first week of training camp.
"I'd say all the way through the offseason, he's been a seasoned pro," Daboll said. "Very fortunate to get him where we got him, he'll continue to get better and better. He's one of the guys that, if Stef gets a down day or something, you're always like, 'all right Gabe, get in there.' You don't need to tell him where he's at, he just goes in and knows."
As far as a rematch with Davis in 2021? Diggs, a first-team All-Pro in 2020, welcomes the competition.
"I tell him all the time now -- 'let me see it,'" Diggs said. "'Last year, you did play pretty well. You did have some success, but there's a lot more football for you and there's a lot more you can obtain, a lot more things you can do better.'
"So let me see that this next year, making that second-year jump."