After stints with the Mariners again in 1995 and 1996, Guetterman played one year for the Sioux Falls Canaries of the independent Northern League.

[3][4] During his time at Liberty, Guetterman set school records that still stood in 2010 for starts (47), innings pitched (334+2⁄3), wins (29), complete games (30), and shutouts (seven).

[5] That same year, the Seattle Mariners selected him in the fourth round of the Major League Baseball (MLB) Draft.

He made 13 starts for the ballclub, accumulating a 6–4 record, a 2.68 ERA, 55 strikeouts, 44 walks, and 85 hits allowed in 84 innings pitched.

[7] He joined the Bakersfield Mariners of the Single-A California League in 1982, making 26 starts and posting a 7–11 record, a 4.44 ERA, 82 strikeouts, 69 walks, and 172 hits allowed in 154 innings pitched.

[7] Guetterman spent most of the 1984 season with the Double-A Chattanooga Lookouts of the Southern League, making 24 starts and posting an 11–7 record, a 3.38 ERA, 47 strikeouts, 38 walks, and 174 hits allowed in 157 innings.

[8] He made his major league debut as a relief pitcher on September 12, allowing one run in 1+2⁄3 innings pitched in an 8–1 loss to the Texas Rangers.

[7] In 1986, Guetterman made the Mariners' roster out of spring training and spent most of the season as a relief pitcher with the major league club, though he started four games for Calgary as well.

[7][10] Sixteen of his 41 appearances for Seattle were multiple-inning efforts, such as a game on May 11, when he pitched five scoreless innings of relief in a 4–3 loss to the Toronto Blue Jays.

[13] Not even invited to 1987 spring training, Guetterman began the season in the bullpen at Calgary, posting a 5–1 record and a 2.86 ERA in 16 appearances (two starts).

[4] After the season, on December 22, he was traded to the New York Yankees with Clay Parker and Wade Taylor for Steve Trout and Henry Cotto.

[19] Used as a starter again for the Triple-A Columbus Clippers of the International League, he made 18 appearances, posting a 9–6 record, a 2.76 ERA, 49 strikeouts, 26 walks, and 109 hits allowed in 120+2⁄3 innings.

[4] Expected to begin the 1989 season with the Clippers, Guetterman made the Yankee roster out of spring training because Ron Guidry suffered a left elbow injury.

Then, Guetterman was manager Dallas Green's choice in April to be the Yankee closer when Dave Righetti slumped due to elbow problems.

[24][25][26] Guetterman would be unscored upon for his first 19 games of the year, pitching 29+2⁄3 consecutive scoreless innings before he gave up five runs to the California Angels on June 4.

[25] In 70 games (all in relief, he would never make another start in the major leagues), Guetterman had a 5–5 record, 51 strikeouts, 26 walks, and 98 hits allowed in 103 innings pitched.

[37][38] However, as the season wore on, he was used less as Steve Howe and Greg Cadaret emerged as the Yankees' primary left-handed relief choices.

"The frustration of not being used has led him to question his long-term desire to remain in New York," explained Jeffrey Moorad, the lawyer and agent for Guetterman.

"His wildness and his penchant for throwing fat pitches kept his seat in the bullpen filled," wrote Jack Curry of the New York Times.

His combined totals between the two New York teams were a 4–5 record, two saves, a 7.09 ERA, 20 strikeouts, 27 walks, and 92 hits allowed in 66 innings.

"[3] The Los Angeles Dodgers signed Guetterman to a contract on January 13, 1993, but he was released at the end of spring training on March 30.

[4] Assigned to the Triple-A Louisville Redbirds of the American Association, he had a 2–1 record, two saves, a 2.94 ERA, 20 strikeouts, 12 walks, and 35 hits allowed in 33+2⁄3 innings pitched.

However, he got Pedro Castellano to ground into a double play to end the game, earning him his sole save of the season in the victory.

[4] He made 12 relief appearances for Calgary, posting a 4–0 record, two saves, a 2.75 ERA, 17 strikeouts, three walks, and 19 hits allowed in 19+2⁄3 innings.

[7] On August 15, the Mariners purchased his contract from Tacoma, sending Bill Krueger to the minor leagues to make room for him.

[4] After beginning the 1996 season with Tacoma, Guetterman was called up by the Mariners on May 28 when Tim Davis broke his left leg.

He gave up a single to Jorge Fábregas and a walk to Gary Disarcina, but he got Darin Erstad to hit into a force play without a runner scoring.

[53] On July 14, Guetterman was designated for assignment to make room on the roster for Ken Griffey Jr., who was coming off the disabled list.

[4] With Tacoma, he made 25 appearances, posting a 2–2 record, a 3.77 ERA, 28 strikeouts, 10 walks, and 27 hits allowed in 28+2⁄3 innings pitched.

"I came to the realization that I didn't have Jesus as my Lord and Savior," he said, due to the preaching and spiritual study he received while a Liberty student.