Alex Jackson, the sixth overall pick in the 2014 First-Year Player Draft, was impressive in his professional debut on Thursday, as the 18-year-old collected two hits and a walk in the rookie-level Mariners' 10-8 defeat of the Padres in the Arizona League.

Serving as the team's designated hitter, Jackson went 2-for-4 with a triple, a run, a walk and two RBIs. He was primarily a catcher in high school but is expected to transition to the outfield in the Minor Leagues.

In Jackson's first professional at-bat, he singled up the middle. He came around to score on an RBI single by the Mariners' 2014 second-round pick Gareth Morgan, who finished 1-for-3 with two walks and three RBIs in his pro debut. Jackson struck out in his next two plate appearances -- once swinging and once looking -- before walking and scoring in the seventh inning. He rounded out his night with an RBI triple in the eighth.

Jackson officially signed with the Mariners on Monday for a reported $4.2 million. He made his professional debut three weeks to the night after he was drafted.