Mariners pitcher Taijuan Walker, who was named the fifth-best prospect by MLB.com this offseason, endured a rocky start to his season at Double-A Jackson.

Walker had a hard time keeping the ball in the park as he allowed two home runs in his minor-league season debut Thursday. The right-hander was charged with four runs on five hits in five innings of work. He also struck out eight and walked four in 91 pitches, 55 strikes.