Cosart bruised his right knee after being knocked over by third baseman Martin Prado. He also allowed a triple and a walk to go along with three strikeouts.
"Everything felt great," Cosart said. "The fastball had really good angle on it. It was down. It was hard, crisp."
But with two outs, the inning nearly became disastrous on a ball Washington's Brendan Ryan slapped down the first-base line. Ryan sprinted to second, and right fielder Giancarlo Stanton's throw was off the mark. Prado went into short left field to back up, and Cosart was caught in an awkward spot.
Seeing an unoccupied bag, Ryan sprinted to third as Prado and Cosart also dashed to the base. Prado ended up rolling onto Cosart's knee.
"Bruised, probably," said Cosart, noting there is no ligament damage. "My calf was a little tight facing the last batter. It was a little tough to push off. But I'm not coming out of my first Spring Training game in my first inning.
"It's one of those in-between plays. We're not supposed to be in no-man's land on that play. I was supposed to be backing up third."
After throwing a few warmup pitches, Cosart remained in the game and issued a walk, but he got out of the jam by striking out Logan Schafer.
In all, Cosart fanned three, all swinging through fastballs that ranged from 93-96 mph. He threw 27 pitches, with 15 strikes.
Since the start of Spring Training, Cosart has been working with pitching coach Juan Nieves and vice president of pitching development Jim Benedict on getting more downward tilt on his fastball.
"They've really got some angle on the fastball," Cosart said. "I haven't missed a lot of bats in the past with my fastball because usually I've been up in the zone, even with my movement. I've been a contact guy."
Cosart's strikeouts per nine innings last season was 6.07.
The mechanical adjustment is keeping his front side closed longer, and his right hand is more on top of the ball, which leads to the downward movement instead of flattening.
Benedict, formerly with the Pirates, informed Cosart that Pittsburgh right-hander Gerrit Cole once had a similar issue.
"Now with the added angle, I saw a lot more swings and misses," Cosart said. "A lot of really bad swings at fastballs in the zone."