But when the Blue Rocks staff finally allowed the right-hander to begin utilizing the secondary pitch once again, the move paid off.
Billo allowed just two hits and one walk over seven shutout innings in Wilmington's 7-0 win over Potomac on Monday. The 21-year-old added five strikeouts in his longest outing of the 2012 season.
"It was the second night that I was allowed to mix in the slider," he said. "It was taken away at the beginning of the season, when the coaching staff wanted me to focus on my other stuff.
"I kind of always knew I could pitch it, though. It was a decent pitch for me before I was drafted [by the Royals in the 28th round in 2010], so I was talking to our pitching coach, Steve Luebber, about mixing in the slider and he thought it would be a good idea too. It worked tonight, that's for sure."
Potomac's Rick Hague singled in the first and Michael Taylor doubled in the second. Then Billo retired 17 of the final 18 Nationals hitters he faced, including nine straight from the fifth through seventh innings.
The Illinois native, who led the Midwest League with a 1.93 ERA over 27 games last season, needed something to jolt his 2012 campaign. After his first seven starts of the season, Billo held a 5.35 ERA for Wilmington. That number swelled to 5.58 after allowing five earned runs over 6 2/3 frames -- despite the 2012 premiere of the slider -- in a 7-5 win over Lynchburg on May 16.
But Billo seemed to think Monday's outing, which dipped his ERA to below 5.00 (4.75) for the first time since April 20, signaled a turnaround.
"It was by far my best outing of the year," he said. "I'm going to take everything I can away from the outing and try to replicate it going forward. [Wilmington catcher] Kevin David and I were working really well, so I'm pleased with how things are going."
The key for Billo might be the ground ball. In starts in which he has a groundout-to-flyout ratio of greater than 2.00 -- it was 2.25 on Monday -- he owns a 1.59 ERA. In all other starts, the mark stands at 6.53.
Leondy Perez struck out two in two perfect innings of relief behind Billo in Wilmington's win.
Left fielder Brian Fletcher went 3-for-4 with a double, two RBIs and a run scored to lead all hitters.