The surging Orioles (6-6) look to sweep a four-game series from the Royals (3-9) on Sunday and prolong Kansas City's recent misery at Camden Yards.
Baltimore won its third in a row and reached .500 after a 1-4 start by beating Kansas City 6-4 on Saturday.
Already assured of a winning homestand, the Orioles will try for a seventh straight home victory over the Royals since a 10-8 loss on May 8, 2005.
The Orioles are hoping they'll have a chance for the sweep, but rain is in the forecast Sunday.
"If you think about it as an audition, it's like it's a do-or-die situation. It's not that in any sense," said Guthrie, who was claimed off waivers from Cleveland in January. "It's me stepping in trying to fill in for the team and help us out at the same time.
"Hopefully I pitch well enough to fill that role anytime it's necessary this year."
Guthrie has allowed two runs and eight hits in 5 2-3 innings out of the bullpen this season. His only other big-league start came against Kansas City on Aug. 12 while with the Indians. Guthrie allowed four runs and five hits in 4 2-3 innings, but did not earn a decision a 6-5 loss to the Royals.
He has a 6.10 career ERA in 10 1-3 innings against Kansas City.
Baltimore has pitched well in the weekend set, allowing five earned runs with a 1.61 ERA.
Utility infielder Chris Gomez hit a grand slam and Brian Roberts, Miguel Tejada, Kevin Millar and Alberto Castillo each had two hits Saturday as Baltimore collected a season-high 13 hits giving them 37 over the last three games.
"We're getting better, for sure," Baltimore Sam Perlozzo told the Orioles' official Web site about his offense which has outscored the Royals 16-6 in the series.
Roberts, who is hitting just .204 from the leadoff spot, is 5-for-13 in the series. Millar is 5-for-9 with three runs versus the Royals and has hit safely in eight straight games.
Kansas City hopes right-hander Zack Greinke (1-1, 1.38 ERA) can build off his most recent start. Greinke, who pitched only three games last season while dealing with depression and social anxiety, allowed one run and six hits in six innings of a 6-3 win at Toronto on Tuesday.
"I have a better mind-set," he said. "I'm just confident and always take the mentality that I'm going to do better than the hitter or that I'm better than the hitter if I make my pitches."
He will need that approach against Baltimore, a team he is 0-2 with an 11.88 ERA in two career starts that both came in 2004.
On Saturday, Mark Grudzielanek went 2-for-4 with two runs and Reggie Sanders and Ross Gload each drove in runs for the Royals, who have lost four in a row and are 1-5 on their 10-game road trip that concludes with three games in Detroit starting Monday.