It was the second tie in three games for San Diego.
After logging 12 victories with a 3.87 ERA as a rookie in 2007, Bannister lost 16 games last season, enduring a 13-start winless streak during one stretch as his ERA escalated to 5.76.
"It's good to get the butterflies again," said Bannister, who turned 28 on Saturday. "Everything went well today. It is exactly how you wanted it to start."
Bannister is in competition for a slot at the rear of the Royals rotation.
Kevin Correia, a non-roster invitee who is making a push for the No. 4 spot in the San Diego rotation, gave up a home run to Guillen to lead off the second. That was the only hit he allowed in two innings.
Correia made 19 starts and six relief appearances last season for San Francisco and was 3-8 with a 6.05 ERA.
"It's a great opportunity for me," Correia said. "It's the first time you've seen really a live hitter with a ball and strike count, and you just want to throw some strikes and I think I did that for the most part."
The Royals signed OF Shane Costa, 2B Alberto Callaspo, C Brayan Pena, 1B Ryan Shealy and RHPs Robinson Tejeda and Julio Pimentel to one-year contracts. The only unsigned Royals are 1B-DH Billy Butler, SS Mike Aviles and OF Mitch Maier.