"It's a coin flip," manager Ned Yost said.
The decision on the reserve catcher behind Salvador Perez will be made by Friday, when the Royals break camp, according to Yost.
"It's going to go down to: do we want a right-handed bat [Hayes] or a left-handed bat [Kottaras]?" Yost said. "They've both done a nice job. What fits our team better? They've both done a nice job offensively and defensively, so it's a tough call."
Both veteran catchers are out of options. The other catcher still in camp, Max Ramirez, was reassigned to Minor League camp on Thursday. Ramirez has logged most of his time at first base and designated hitter rather than catcher this spring, batting .318 (14-for-44) with 14 RBIs.
Yost announced on Thursday that Gutierrez won out over two other right-handers, Louis Coleman and Dan Wheeler, for the seventh and last relief job.
A one-time closer for the D-backs, Gutierrez came back last year in the Royals' Minor League organization after having Tommy John surgery in September 2011. He had an outstanding winter season for Caracas and was named Reliever of the Year in the Venezuelan League.
In 12 outings of one inning each in the Cactus League, Gutierrez had a 4.50 ERA, but he was especially impressive in his last two appearances -- five strikeouts in two innings.
"He really stepped up the last couple of times," Yost said. "It shows us what he can be. He's a strike-throwing machine -- look at his numbers, 19 [strikes] out of 24 [pitches] yesterday. Huge strikes again. Really good breaking ball, 95 mph fastball that he spots well."
Gutierrez also had the advantage of being out of options, meaning he likely would have been picked up off waivers by another team. Coleman was optioned to Triple-A Omaha, and Wheeler, as a non-roster player, was assigned to Minor League camp and will pitch for Omaha.
Wheeler, in 11 innings, had a 0.82 ERA, giving up 13 hits but just one run. He also notched 14 strikeouts against one walk. A 13-year veteran, Wheeler pitched part of the season for Cleveland last year.
Coleman worked 12 1/3 innings with a 1.46 ERA. He gave up two runs, nine hits and two walks, with eight strikeouts. He's pitched to a 3.25 ERA in 90 games for Kansas City over the last two years.
In the bullpen, Gutierrez joins closer Greg Holland, Aaron Crow, Kelvin Herrera, Tim Collins and former starters Luke Hochevar and Bruce Chen. Collins and Chen are the left-handers, but there's no "situational left-hander," a southpaw whose main function is to face left-handed batters.
"We don't need 'em. We've got Herrera and Crow, who are both very proficient at getting left-handers out," Yost said. "Would I like to have another lefty? Yeah. But I've gone years -- especially at Milwaukee -- two years when I didn't even have a lefty. If you've got righties that can get lefties out, you're OK."
Yost said he's very happy about the makeup of his relief corps, although there have been recent concerns about poor outings by Collins and Hochevar.
After giving up seven runs in his two previous innings, Collins worked two-thirds of a scoreless inning in Wednesday night's 10-inning, 9-9 tie with the Cubs. Hochevar, however, was rocked for five runs in two-thirds of an inning after not allowing a run in his previous five innings.
"You're going to go through little dead-arm periods when you're just not sharp," Yost said on Thursday morning. "Last night was one for Hoch. I thought his location was good, his pitches were good. I just didn't think they were quite as sharp as they had been.
"We've have had a phenomenal spring from the bullpen. I think last night was the first hiccup we've had all spring -- in the late innings, really."
On Wednesday, Yost had decided to retain veteran Miguel Tejada over the less experienced Irving Falu as a backup infielder to pair with Elliot Johnson. Evaluation time on both Tejada and Falu was lost when both were absent 17 days for the World Baseball Classic.
"Tejada's a better fit," Yost said. "Tejada can play third, second, first and can play some short. We've got Elliot, who can play all over the field. We're covered greatly in that department."
Jarrod Dyson is the reserve outfielder.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.