The No. 1 defense in the NFL got a major upgrade on Friday with the addition of former Pro Bowl tackle Sheldon Richardson, who provides the Minnesota Vikings with an immediate boost at the 3-technique spot, a priority entering free agency.

A source told ESPN's Adam Schefter that Richardson signed a one-year contract.

When Tom Johnson and Shamar Stephen hit the open market on Wednesday afternoon, only 58 snaps from last year remained on the roster at the second defensive tackle spot. Finding a sturdier option to plug in next to nose tackle Linval Joseph was a priority they were able to fill with Richardson, who previously played with the Seattle Seahawks and New York Jets.

Richardson is the second Pro Bowler the Vikings have signed in as many days; quarterback Kirk Cousins inked his contract on Thursday. Minnesota's starting front four in 2018 could yield Danielle Hunter, Joseph, Richardson and Everson Griffen.

Acquiring Richardson in Week 1 of free agency will allow the Vikings to use their first-round draft pick elsewhere, namely in search for an offensive lineman.

The Vikings were confident that they were in good position with Richardson once he arrived in Minneapolis on Thursday. The defensive tackle dined with Cousins and Vikings brass and spent the rest of the day touring the new team headquarters in Eagan.

A move the Vikings made Thursday night aided their ability to sign the sixth-year tackle. Minnesota restructured the contract of veteran running back Latavius Murray so his $5.15 million salary wouldn't become guaranteed on Friday.

Seattle acquired Richardson in a trade with the Jets right before the start of the 2017 season, sending receiver Jermaine Kearse and a second-round pick in 2018 to New York. The teams also swapped 2018 seventh-round picks.

Richardson started 15 games for Seattle, missing one with an injury, and was more impactful than his lone sack might suggest. Richardson, who turns 28 in November, had a hand in three of the biggest defensive plays of Seattle's season -- an interception and a fumble recovery in a victory over the Los Angeles Rams in October, and a strip of quarterback Carson Wentz to save a touchdown against the Philadelphia Eagles in December.

By the end of the season, coaches were noting how Richardson was adjusting well to Seattle's 4-3 defense, which he admitted had taken some time after playing in a 3-4 during his first four seasons. Richardson expressed his desire to return to the Seahawks.

ESPN's Brady Henderson contributed to this report.