The temperature climbed to 65 degrees at game time in Clinton, but LumberKings right-hander Edwin Diaz brought most of the heat Wednesday night at Ashford University Field.
The Mariners' No. 4 prospect reached 96 mph with his heater and racked up eight strikeouts over five scoreless innings as Class A Clinton shut down Lake County, 4-1 in the Midwest League.
Diaz (1-0) allowed two hits en route to his first win in full-season ball. Through two starts, the 20-year-old has struck out 13 and walked four over 9 2/3 innings while compiling a 1.86 ERA.
Clinton pitching coach Cibney Bello said the Puerto Rico native worked mostly between 93-95 mph with his fastball, racking up 11 swing-and-misses.
"Pretty much he was just pounding the zone," Bello said. "His fastball was really good today, very effective. ... It had good life today. Some of them had some sinking action down in the zone."
Beyond that, Diaz worked in both his slider -- a pitch MLB.com's prospect folks ranked as above average -- and a developing changeup. Bello said he's hoping to see improvements from the change as the season unfolds.
"He threw a couple today that were good, down in the zone," Bello said. "I think he's going to get better with it."
Diaz struck out two in the first inning and another in the second while allowing a hit and a walk. In the third, Cody Ferrell reached on an error to start the frame. Two batters later, Paul Hendrix walked, but Diaz stranded both runners by striking out Grant Fink and getting Anthony Santander to fly to center.
After getting two more strikeouts in the fourth, Diaz concluded his outing with a 1-2-3 fifth, fanning Brian Ruiz and Ferrell.
The 2012 third-round pick drove up his prospect stock in 2013 with Rookie-level Pulaski, where he issued 18 walks over 69 innings. A year earlier, he walked 17 batters over 19 innings in the Arizona League.
Diaz has walked two batters in each of his first two starts for the LumberKings. His command has been good, Bello said, because of mechanical consistency and a willingness to pound the zone with that mid-90s heater.
The hurler also has worked on adding weight since he was drafted. Signed at 6-foot-2 and 165 pounds, Diaz has added about 25 pounds since, MLB.com reported in its Mariners prospect rankings. He threw 78 pitches on Wednesday and should work with a pitch count around 80 through the early part of the season.
"He's been working really hard in the complex, putting on weight," Bello said. "He's more mature. He's getting used to his routine and is now putting everything together, getting really good results."
Diaz's batterymate, Marcus Littlewood, went 1-for-1 with three walks and also caught a runner stealing. The 2010 second-round pick is batting .500 with a 1.146 OPS through five games.
Mariners 2012 second-rounder Joseph DeCarlo slugged his first full-season homer, a two-run shot in the fourth.
Robbie Aviles worked the final three innings for Lake County, yielding one hit while striking out five.