SANTA CLARA, Calif. -- San Francisco 49ers general manager John Lynch teased it late Saturday night, but it didn't become official until Sunday: The Niners are keeping fullback Kyle Juszczyk in the fold.

With the goal to re-sign Juszczyk before the early negotiating window opens Monday, the Niners and their versatile fullback agreed to a five-year, $27 million deal that includes $10 million guaranteed, a source told ESPN's Adam Schefter on Sunday evening.

Joe Linta, Juszczyk's agent, confirmed via Twitter that a five-year deal had been reached.

The agreement with Juszczyk comes less than 24 hours after Lynch sent a cryptic tweet Sunday night that said, "I'm thirsty. Niners fans, you want some 'Juice?'" Lynch's tweet was a clear reference to Juszczyk, who goes by the nickname "Juice" and has become a fan favorite in the Bay Area and in the Niners' locker room.

"He is, in my opinion, one of one," tight end George Kittle said at the end of the season. "I don't know that anyone does the things that he does on the football field. I also think he's incredibly underappreciated. But people that watch football, the people that understand football, they get how important Juice is."

Juszczyk also confirmed the five-year deal, thanking the organization on social media Sunday night.

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San Francisco has more than 20 players set to become unrestricted free agents and has prioritized about a half-dozen of them going into the new league year. Keeping Juszczyk allows the 49ers to continue working toward deals with their other top priorities, including left tackle Trent Williams and cornerbacks K'Waun Williams and Jason Verrett.

The 49ers initially signed Juszczyk to a four-year, $21 million deal in 2017, a contract that easily surpassed any previous deal for a fullback. In four seasons since, Juszczyk's 102 receptions for 1,080 yards and seven touchdowns dwarf the 43 catches, 399 yards and four scores of the next-closest fullback in each of those categories.

Juszczyk's versatility has become a focal point of Shanahan's offense, which emphasizes making things look similar in terms of personnel and alignment but adding wrinkles that throw off the defense. Juszczyk had embodied that by lining up in the slot (9.3% of his snaps), outside receiver (7.2%), inline tight end (11.5%) and in the backfield (72%).

Coach Kyle Shanahan's offense has deployed a fullback more than any team in the league since acquiring Juszczyk and has had far more success with him on the field.

With two running backs on the field, the 49ers have averaged 5.99 yards per play (second in the NFL), 4.49 yards per rush (fifth) and 8.65 yards per pass (third). With one or no running backs on the field, those numbers drop to 5.45 (20th), 4.26 (23rd) and 6.48 (19th).