After graduation, Armas spent 1994 and 1995 playing for the USISL's Long Island Rough Riders, being selected as a USISL All-Star. In 1995, the Rough Riders defeated the Minnesota Thunder in the USISL's Pro League Championship. Besides Armas, the 1995 Rough Riders also included such future MLS standouts like Tony Meola, Giovanni Savarese and Jim Rooney. In 1996, Armas was drafted by Los Angeles Galaxy in the first round of the Major League Soccer Supplemental Draft, and played a significant role in their first and second seasons. Chicago Fire acquired Armas in a trade for their inaugural 1998 campaign. It was with the 1998 Chicago Fire team that Armas emerged as an exceptional player, helping them win their first MLS Championship that year. Between 1998 and 2001, Armas was named to the MLS Best XI four consecutive times, his streak only being broken by an ACL injury that kept him out of much of the 2002 campaign; Armas was named to his fifth Best XI after the 2003 MLS season, in addition to being named the MLS Comeback Player of the Year. He was named U.S. Soccer Athlete of the Year in 2000. In ten years in MLS, he totaled 11 goals and 41 assists, plus added four goals and four assists in the playoffs. On April 19, 2007, Armas announced that the 2007 MLS season with the Chicago Fire would be his last, as he decided to retire. His retirement was made official on November 13, 2007, after spending 12 years in MLS.
International
Armas played for Puerto Rico in the 1993 Caribbean Cup. The competition was not then recognized by FIFA and so his five matches were classed as friendlies. He was therefore later allowed to switch his allegiance to the United States, for whom he made his debut November 6, 1998 against Australia. He went on to register 66 caps. Unfortunately for Armas, he did not break into the squad until soon after the 1998 FIFA World Cup, and his ACL injury came just before the 2002 FIFA World Cup, so he was never able to play for the United States in the world's most prestigious soccer competition. He was named as a standby player for the 2006 FIFA World Cup, and did not feature in the final squad.
Coaching career
On July 6, 2018, Armas was promoted to head coach of the New York Red Bulls after former manager, Jesse Marsch departed the club.
Personal
Armas and his wife, Justine, have two sons, named Christopher and Aleksei. Armas currently serves as head coach for the New York Red Bulls. Armas formerly served as an assistant coach for the Chicago Fire in 2008, and was the head women's soccer coach at Adelphi University between 2011 and 2015. He also taught physical education at St. Anthony's High School in South Huntington, New York, the high school from which he graduated.
