<P> In years in which the AL East plays the NL East and the AL West plays the NL West (2015, 2018, etc .), the teams play their assigned "rival" for the year six times and the other "rival" either three or four times . </P> <Ul> <Li> Baltimore Orioles v. Philadelphia Phillies--Played from 1997 to 2005 . In 2006, the Washington Nationals replaced the Phillies as the Orioles' rival . Although the Nationals moved to Washington in 2005, the schedule for that season was already established, so the Washington - Baltimore rivalry series could not start until the next season . Therefore, in 2005 the Orioles played the Phillies as their rival for the last time, while Washington played Montreal ′ s planned 2005 schedule, which included what would have been the Expos ′ s interleague rivalry games with the Toronto Blue Jays . </Li> <Li> Houston Astros v. Texas Rangers (Lone Star Series)--Played from 1997 to 2012 . In 2013, the Astros moved to the American League West, and the two teams began play against each other 19 times a year as divisional rivals . </Li> <Li> Montreal Expos v. Toronto Blue Jays (Pearson Cup or The All - Canadian Series)--Played from 1997 to 2004 (and by Washington against Toronto in 2005). By the time the Expos moved to Washington, D.C., to become the Washington Nationals for the 2005 season, the 2005 schedule already had been set, so the Nationals played what had been intended as Montreal ′ s rivalry series with the Blue Jays that season . In 2006, the Nationals began playing the Baltimore Orioles annually as their interleague rival . </Li> <Li> San Diego Padres v. Seattle Mariners - Played as a result of the teams sharing a Spring Training complex in Peoria, Arizona, this matchup occurred every year from 1997 to 2015, but has been treated as a split rivalry since 2016 . Often cited as a counterargument against "rivalry" series in general due to the teams' lack of a historical rivalry and their locations on opposite ends of the Pacific Coast (and the I - 5 corridor), as well as both teams' general underachievement throughout their time as "rivals" (never made playoffs in the same season during that span). Sometimes jokingly referred to as the Vedder Cup after Pearl Jam singer Eddie Vedder, who has lived in both cities (although Vedder himself is a Chicago Cubs fan). </Li> </Ul> <Li> Baltimore Orioles v. Philadelphia Phillies--Played from 1997 to 2005 . In 2006, the Washington Nationals replaced the Phillies as the Orioles' rival . Although the Nationals moved to Washington in 2005, the schedule for that season was already established, so the Washington - Baltimore rivalry series could not start until the next season . Therefore, in 2005 the Orioles played the Phillies as their rival for the last time, while Washington played Montreal ′ s planned 2005 schedule, which included what would have been the Expos ′ s interleague rivalry games with the Toronto Blue Jays . </Li> <Li> Houston Astros v. Texas Rangers (Lone Star Series)--Played from 1997 to 2012 . In 2013, the Astros moved to the American League West, and the two teams began play against each other 19 times a year as divisional rivals . </Li>

When do the astros play their first game