CHICAGO — Jake Diekman threw 65 pitches in four of the Phillies' first five games, so he will likely be excused from the sixth on Sunday. The lanky lefty emerged, in less than a week, as Ryne Sandberg's most trusted middle reliever for tight situations. There is an obvious reason.

"Unbelievable," outfielder Marlon Byrd said. "He brings that fire."

Diekman fired 10 pitches at 94 m.p.h. or harder Saturday. His velocity rose in 2013 with improved mechanics and confidence. Just two lefthanded relievers — Tampa's Jake McGee and Pittsburgh's Justin Wilson — have thrown their fastballs in 2014 at a higher average velocity than Diekman's, according to FanGraphs.

Speed in the post-steroid era, where strikeouts are up and runs are down, is a dangerous weapon. And Diekman, who hit 99 m.p.h. at times last summer, could gain more later in the season.

Last week, Sandberg said Antonio Bastardo is his "eighth-inning guy," although Diekman could challenge that status. Diekman pitched in the eighth inning Sunday with a two-run lead because Sandberg thought Bastardo struggled with the cold weather during his outing Friday.

"His stuff plays when he works ahead in the strike zone," Sandberg said of Diekman. "He's pitching with confidence."

Diekman was the first Phillies pitcher to appear in four of the team's first five games since Danys Baez in 2010. Twelve pitchers since 1987 equaled that workload.

He allowed runs in each of his first two outings, although two scored on opening day when Sandberg tried to use Diekman for more than one inning. The manager has found high-leverage situations for Diekman from anywhere between the sixth and eighth innings.

Byrd doubled against Diekman last season in their only meeting. He can see why most hitters have trouble.

"It's an uncomfortable at bat," Byrd said. "From last year, I remember he would pound the zone early. Fastballs in. Then he'd start guys off with sliders, giving them something else to think about. That year of knowledge always helps."

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