Teams traditionally line up their ace starters to pitch on Opening Day in order to get the season started off right. If team schedules aligned perfectly, we’d see the aces square off against each other every fifth day; but injuries, off days, trades, and general ineffectiveness often jumble up the rotation and fans don’t get to see as many marquee matchups. But how often do two teams’ Opening Day starters face fellow aces?

In 2009, the 30 Opening Day starters combined for 824 starts, and around 20% were against fellow #1 starters, more than any other single rotation spot. However, a surprising 31% of their starts come against pitchers who weren’t even in the opposing team’s starting rotation to start the season! Here’s the breakdown by rotation slot:

Some starters oppose more fellow aces than others. Justin Verlander faced the opposition’s ace 11 times in 35 starts, the most in the majors. The runner-up was Brad Penny, who faced 9 aces during his 24 starts with the Red Sox but just one in 6 starts with the Giants. Penny went 7-8 for Boston but 4-1 while with San Francisco. (He also cut his ERA in half, which surely played a role in the improvement.)

Here’s the list of starters who faced the most aces in 2009:

Cy Young contenders Justin Verlander, Adam Wainwright, and CC Sabathia all racked up high win totals despite facing fellow aces quite frequently. It helped that they had powerful offensive support as well.