The 18-year-old allowed two runs on two hits while striking out seven and walking one in his first career complete game as the Class A Clinton LumberKings beat the Great Lakes Loons, 6-2.
The Mariners No. 4 prospect gave up a two-run homer to Blake Dean in the first inning at Alliant Energy Field before shutting the Loons down the rest of the night.
He retired the next nine batters without allowing the ball to leave the infield before Chris Jacobs hit a one-out single to right field with one out in the fourth. After that, Walker, selected 43rd overall in the 2010 Draft, was perfect over the last 5 2/3 innings, retiring the final 17 batters he faced.
Walker is the first Clinton hurler to throw a nine-inning complete game since right-hander Kenn Kasparek accomplished the feat on Aug. 3, 2009 in a 5-0 win over Burlington. Walker's previous longest outing was 7 2/3 innings, set May 31 in a 10-inning, 4-3 win on the road in Fort Wayne.
The right-hander, who fanned 11 over six innings of one-hit ball in Thursday's 3-0 blanking of the Cedar Rapids Kernels, improved to 4-4 with the victory. His 2.66 ERA would rank 10th in the league if he had enough innings to qualify. Wednesday's outing marked the seventh time in 13 starts the California native has yielded three or fewer hits.
Ryan Christenson (7-6) allowed six runs -- five earned -- over three innings in the losing effort.