"You take your chance right there, and with our bullpen we figured we could hold it and we did," Yost said after a 4-3 loss to the St. Louis Cardinals on Thursday night. "We just couldn't get that one extra run we needed."
The Royals went on to put runners on second and third with no outs, but Rosenthal held on for his 30th save in 32 chances. Mike Moustakas grounded out to end it.
Yost was surprised by the Cardinals decision to play the infield in and allow two runners to take second without a play, both calls ruled defensive indifference.
"There's nothing you can do differently," the manager said. "We needed to execute there, and of course that's easy for me to say.
"Anytime you're going to let the winning run waltz to second base ... they've got a lot of confidence in their closer."
As in the originally scheduled game, St. Louis and Kansas City led their league in wins and Lackey (9-5) and Young (8-6) were the scheduled starters.
Young gave up four runs in three innings, his shortest outing since he allowed five runs while getting just two outs for Seattle last Sept. 1 at Oakland. He struggled with control and had no issue with getting pulled for pinch hitter Kendrys Morales, who flied out with two on to end the fourth.
The 6-foot-10 right-hander has surrendered 14 homers, half of them on two-strike counts.
"I understood the situation," Young said. "I absolutely had no problems with it. It was the right decision."
Paid attendance of 46,003 was the 24th sellout for St. Louis, which took the season series 4-2, but there were several thousand no-shows for the opener of an elongated 11-game homestand. Both teams wore throwback jerseys from the 1985 I-70 World Series won by Kansas City in seven games.
Salvador Perez and had consecutive RBI singles in the first for the Royals, but they managed just two more hits in Lackey's final six innings. The 36-year-old right-hander is 5-1 with a 1.75 ERA in his last eight starts, working seven or more innings in all but one of them.
Carpenter's 10th homer, and just his second in two months, put the Cardinals ahead 4-2 in the third. Grichuk, who also singled and flied out to the wall in right, has a team-leading 13 RBIs this month.
The Cardinals are 61-34 overall and 34-12 at Busch Stadium, both major league bests.
Eric Hosmer had two hits and is 13 for 25 during a six-game hitting streak. ... Rios matched his season high with three hits and has 11 hits in his last six games.
Royals: Young has been hindered by back tightness and is 1-3 in his last five starts.
Cardinals: Jaime Garcia threw five hitless innings in his first rehab start for Class A Peoria, the only blemish on his line a hit batter. ... Rookie 1B Stephen Piscotty was a pregame lineup scratch with neck stiffness.
Royals: Jeremy Guthrie (7-5, 5.36) faces the Astros to open a three-game series at home. He's 20-12 with a 3.68 ERA post-break the last four seasons.
Cardinals: Rookie Tim Cooney (0-0, 3.33) faces the Braves, making his sixth career start in search of a first decision. The lefty threw 5 2-3 scoreless innings his last time out, an 18-inning loss to the Mets on Sunday.