The skipper gave a simple reason for the choice of Mendoza.
"He threw better, he had a better spring," Yost said.
Mendoza pitched in three Cactus League games and had a 0.82 ERA, along with a 2-0 record. In 11 innings, he gave up one run, 10 hits and two walks, with eight strikeouts. A sinkerballer, he gave up no home runs. Mendoza missed several days to pitch for Mexico in the World Baseball Classic.
Chen has worked in four games, with a 7.90 ERA and a 1-1 record. While he had 12 strikeouts against three walks in 13 2/3 innings, seven of the 16 hits against him were home runs, including five in his last start.
"You go back into the track records, and there's no denying Bruce has won 35 games in the last three years," Yost said. "Mendy is a guy that has good natural sink on his fastball. His breaking pitches have evolved. And he's gotten better and more consistent. He had a great winter, he's had a great spring. We'll give him the first crack at it."
Mendoza cranked up his arm late this winter in the Mexican Pacific League, and his Obregon team won the title. Then he was named the Most Valuable Player in the Caribbean Series. So winter ball paid off for him.
"I did it with that reason, to come to spring ready to compete, and every start I was on the mound to show them that I could get people out and that I can be consistent in what I'm doing," Mendoza said.
"I'm pitching with great confidence, and that's the main thing. I think I can take that to the big league level and get people out."
Mendoza was in the Royals' rotation for most of last season, making 25 starts. In a total of 30 games, he was 8-10 with a 4.23 ERA.
Chen has led the Royals in victories in each of the last three seasons, although last season his ERA jumped up to 5.07 in 34 starts. His move to the bullpen puts him there with Luke Hochevar, the other most-used starter last season. Their vulnerability increased markedly when the Royals re-signed Guthrie and traded for Santana, Shields and Davis.
Yost said he views Chen initially as a long reliever, although that could evolve into shorter stints, depending on how many innings the new starting rotation can provide.
Chen accepted his new assignment gracefully.
"It's a challenge, and I'm going to try to make the most out of it. I know that Luke took a really good approach, and he's been excelling at that position. It's tough, but it's not impossible," Chen said.
"We have to do everything we can to help this team win. We can't be feeling sorry for ourselves, feeling bad or pouting or anything. That's not going to help the team or us."
Although Chen was supposed to start Tuesday's game against the Mariners, instead he was put on the bullpen list so he could begin adjusting to relief work. Minor Leaguer Sugar Ray Marimon was brought up to start instead.
Chen pitched the sixth inning of an 11-6 victory, loading the bases with one out before pitching out of the jam.
"He got through it, but I was really impressed," Yost said. "Like I told Bruce, it looked like there was two different pitchers out there. One pitcher was out there until the bases got loaded, and then another guy stepped up, and he was a different guy out there. He really got on the attack, got aggressive and got out of the inning."
Yost brushed off any concern that Mendoza gives the Royals an all right-handed rotation. He liked the addition of lefty Chen to the only current left-handed reliever, Tim Collins.
The move emphasizes the Royals' increased depth in starting pitching, too. Chen and Hochevar have starting experience and could easily come out of the 'pen. In the Minors, the Royals have such pitchers as Will Smith, Yordano Ventura, Nate Adcock and Everett Teaford in reserve.
Although it didn't figure in the decision, Mendoza's first start will come in the season's fifth game at Philadelphia, and his sinkerball could benefit the Royals.
"Especially in Philadelphia, you want to keep the ball on the ground, because that's a fly-ball park, that's a short home-run hitters' park," Yost said.
Now, about Mendoza and this long-reliever stuff ...
"He is the perfect long reliever," Yost repeated. "He's the better guy right now and the reason for that is Bruce, like most veteran players, is a little slow to get it going in Spring Training. So starting the season, we wanted to put the guys out there that are doing the best in Spring Training. I'm not saying that it doesn't change somewhere down the road. Who can say what'll happen. That's where we're starting."