Baseball America rated him as the #9 prospect in the Yankee system, one spot ahead of fellow right-hander Tony Armas Jr. Rios spent most of 1997 with Columbus, doing an effective job, if not as impressive as his prior three years.

He made his major league debut in rough form on May 30, relieving Ramiro Mendoza with two on and one out against the Boston Red Sox.

He promptly served up back-to-back home runs to Wil Cordero and Mo Vaughn, the first two batters he faced.

He returned to Columbus but came back to the Yankees for a game late in the year, replacing Hideki Irabu with one on and one out in the 7th inning on September 5.

After back-to-back singles to open the 8th, he was replaced by Graeme Lloyd, ending a horrible rookie year in the majors – 9 hits and 5 runs in 21⁄3 innings plus three inherited runners plated.

He went 6–7 with one save and a 5.63 ERA for the 1998 Omaha Royals, being used regularly as a starting pitcher for the first time in his professional career.

Rios drew notice overseas and was picked up by the KIA Tigers of the KBO League in 2002.

He battled control problems, walking 147 in 2051⁄3 innings pitched, but also tied Bae for the KBO lead in strikeouts (also 147).

He was the first foreigner to win 20 games in a year (not counting Japanese natives of South Korean descent).

He won five more games than runners-up Ryu Hyun-jin and Kenny Rayborn, and his ERA was 0.77 was ahead of runner-up Chae Byung-ryong.

Rios became the fifth pitcher in KBO history to have won 10+ games in six consecutive seasons, following Kim Si-jin (1983–1988), Sun Dong-yeol (1986–1991), Lee Kang-chul (1989–1998), and Jung Min-chul (1992–1999).