The San Francisco 49ers' defensive front added a major piece on the first day of the NFL's free agency negotiation period.

Javon Hargrave, the No. 1 free agent on NFL.com analyst Gregg Rosenthal's Top 101 list, agreed to a four-year, $84 million deal with the Niners on Monday, NFL Network Insider Ian Rapoport reported, per a source.

Hargrave's deal comes one day after Daron Payne re-signed with the Washington Commanders for $90 million across four years, a pact that helped set the market on the defensive line. The Philadelphia Eagles expected Hargrave to be priced out of their budget, but it's still a big loss inside for the NFL's No. 1-ranked sack unit.

Hargrave, who turned 30 last month, will add to an already-deep front in San Francisco that's anchored by Nick Bosa and Arik Armstead. The 49ers ranked first in defense last season, although they're making a change at defensive coordinator, with Steve Wilks replacing DeMeco Ryans, who is now the Texans' head coach.

The 6-foot-1, 305-pound Hargrave was drafted by the Steelers in the third round of the 2016 NFL Draft. He joined the Eagles as a free agent in 2020, seeing his pass-rush opportunities grow in Philadelphia. Hargrave totaled 23.0 sacks over the past three seasons, including a career-high 11.0 last season.

The 49ers saw firsthand in the NFC Championship Game just how dominant Hargrave can be when he had a sack, five tackles and a pass defensed, helping harass the 49ers' quarterbacks and send the Eagles to Super Bowl LVII.

The 49ers were not expected to be big players in free agency, entering the week with 20 unrestricted free agents and less than $10 million in salary-cap space. But defensive tackle was a concern for the 49ers, and they're always good for a free-agent surprise. Hargrave fits that bill and should make a scary rush unit even better.