Ultimately he chose the team's most consistent starter, but Showalter downplayed the decision, indicating the other starters he considered — Ubaldo Jimenez and Dylan Bundy — could be used in the do-or-die game.
Both will be on the team's 25-man playoff roster for this round, which can be stacked with relievers and reserves for the one game.
"It's a good, tough one, because we've got some people pitching well," Showalter said. "You know, we had probably three options, and Chris is one of those good options. There's not much separator there. We'd feel good about any of the three guys, including Dylan. And all three may pitch in the game."
The Blue Jays, who are 46-35 at Rogers Centre this season but lost two of three to the Orioels there last week, will start right-hander Marcus Stroman.
Stroman, 25, was the Blue Jays' Opening Day starter but pitched poorly before the All-Star break, posting a 4.89 ERA. In August and September, though, the 5-foot-8, 180-pounder has pitched to a 3.28 ERA, despite a 1-6 record.
Manager John Gibbons' selection of Stroman was a bit of a surprise, considering Stroman has a 7.04 ERA in four starts this season against the Orioles.
Another option was trade-deadline acquisition Francisco Liriano, a veteran left-hander who, in his only start against the Orioles this year, struck out 10 batters in 6 1/3 scoreless innings last week.
Liriano, who pitched the Pittsburgh Pirates to a wild-card win in 2013, will likely be available out of the Blue Jays' bullpen, just as some of the Orioles' typical starters might be counted on to mitch middle or late innings.
Showalter admitted he might manage Tuesday's game differently than he has over the course of the season, given the single-game dynamic.
"There is a sense of finality," Showalter said. "There are times during the season you may not put your best foot forward so you can be consistent over the long haul, because of health and putting people in harm's way. Not that we'll do that tomorrow, but there are some differences that you have to grasp. You don't worry about tomorrow or the next day. Everything is about that nine innings or 10 or 11, whatever it might be. There are some times during the course of the game that it may happen earlier than usual, that you may attack it differently."
Still, turning to Tillman, who is 16-6 with a 3.77 ERA in 30 starts this season, isn't much of a surprise, especially if the Orioles are convinced he's healthy coming back from a three-week stint on the disabled list. The Orioles are 22-8 in games started by Tillman, and he's been the rotation's anchor.
He's come through when the team has needed him this year. Three times he earned a win to stop a three-game losing streak; twice he stopped a four-game skid.
"I take every game and approach it the same way," Tillman said. "[Try] not to put any added pressure on yourself. Just go out and try to do the same thing you do every other game."
Tillman came one out shy of a quality start in his last outing — which came Wednesday in Toronto — as he allowed two runs (one earned) over 5 2/3 innings in a 3-2 win over the Blue Jays. In that game, Tillman overcame an early 2-0 deficit and some hiccups, including two errors in the first inning, his own errant pickoff throw being one of them.
"I think anytime you're able to pitch well somewhere or against a certain team, I think it helps a little bit, but I don't buy into that all that much," Tillman said. "Every day is different. Every day you're carrying different stuff. You've got to find a way to navigate every game a different way. I don't dwell on the past too much, but we've played well here this year, and it's been fun. … I have seen them a lot and they've seen me a lot."
Over his career, Tillman has struggled against the Blue Jays and at Rogers Centre, but this season he's pitched better, posting a 3.63 ERA in four starts against Toronto. In two starts at Rogers Centre this year, his ERA is 2.38.
Those numbers are far better than those over his career against the Blue Jays. In 24 career starts against them, Tillman is 5-10 with a 5.44 ERA. His numbers are worse when pitching in Toronto — 2-6 record and 7.01 ERA in 13 starts. Last season, Tillman was 0-4 with an 11.72 ERA in four starts against Toronto.
"There are no secrets," Tillman said. "I don't think I've gone out of my way to do anything different with these guys. It's just the way the cookie crumbles sometimes. Last year didn't go so well; this year has been a little better. I think we're a very solid defensive team, and I think when you have that in the back of your mind as a starting pitcher, you're going to be able to attack the zone and make your defense work."
Tillman will work on two extra days rest, which Showalter said played a role in his decision.
He said he gave strong consideration to Jimenez, who has a 2.45 ERA over his last seven starts and tossed 6 2/3 scoreless innings in his last start Thursday in Toronto. Another option was Bundy, who hasn't started since Sept. 25. His only experience against the Blue Jays this year is 3 2/3 scoreless relief innings.
"Just because someone's not starting a game doesn't mean they can't be real impactful," Showalter said. "And we looked at a lot of guys. We talked about even [Yovani] Gallardo, but he's just had three days off and just really doesn't fit that bullpen feeling."