Even as they have pursed free agents from other teams in an attempt to repair a shoddy defense, the Minnesota Vikings were chasing one of their own unrestricted veterans, and on Thursday they landed him.

Defensive end Lance Johnstone, the team's leading sacker in 2002, has reached agreement on a three-year contract. The deal could be worth as much as $4.6 million, with incentives, and includes a $700,000 signing bonus. The first-year base salary is $655,000.

Later in the day, the Vikings added their second new cornerback in a week, reaching agreement with unrestricted free agent Ken Irvin, who played for the New Orleans Saints in 2002.

Irvin, 30, netted a three-year, $4.5 million contract that that includes a signing bonus of $1.2 million.

The Vikings concluded a busy day by reaching agreement with unrestricted free agent offensive tackle Mike Rosenthal on a two-year deal. Financial details of that contract were not immediately available.

Retaining Johnstone, a seven-year veteran who started all 16 games last season, was a key for the Vikings, whose offseason priority is upgrading the defense. A prototype "edge" rusher, Johnstone is the Vikings' best outside pass rush threat and he registered seven sacks in 2002.

Signed as an unrestricted free agent in 2001, he has 12½ sacks in his two seasons with the Vikings. Johnstone drew interest from several teams during the free agent period, but no one stepped up financially to the level that he was anticipating, and the Vikings remained dogged in their pursuit.

Minnesota coaches feel Johnson can still be a double-digit sack player.

Johnstone, 29, has 41½ career sacks to go with 290 tackles, a dozen forced fumbles, one interception and 15 pass deflections. While not particularly big, he possesses good quickness and plays the run better than most people think.

The former Temple star played the first five seasons of his career with the Oakland Raiders, who chose him in the second round of the 1996 draft, and he totaled 21 sacks for them in 1998-99.

Irvin chose the Vikings over the Detroit Lions, and also had interest from a few other teams as well. The eight-year veteran played the first seven years of his career with the Buffalo Bills, before signing with New Orleans as a free agent last spring.

His addition, along with that of free agent Denard Walker last week, should significantly upgrade the Minnesota cornerback corps. Given what transpires over the rest of free agency, and where the coaches decide to use versatile Corey Chavous, who can play safety or cornerback, Irvin could challenge for a starting job. At worst, he should be the "nickel" corner, a role that he has filled in the past.

The former University of Memphis standout started nine contests for the Saints in 2002 and appeared in all 16. He had 62 tackles, two interceptions and 17 passes defensed. For his career, he has appeared in 124 games and started 63 of them, and has nine interceptions and 63 pass breakups.

Rosenthal, 25, was a key acquisition for the Vikings, who have been seeking a starting right tackle so they can move Chris Liwienski to his more natural position of left guard. Minnesota failed to land Orlando Brown, their main target, last week and then turned its attention to Rosenthal.

A four-year veteran who has played his entire previous career with the New York Giants, the former Notre Dame star emerged as a solid performer in 2002, his first full season as a starter. After starting just nine games in his first three seasons, he started all 16 last year.

Len Pasquarelli is a senior writer for ESPN.com.