Now both starters are division rivals, and Colon will make his New York Mets debut at home Wednesday night against Gonzalez and the Washington Nationals, who will face a Mets team that just lost its closer.
Colon went 28-15 with a 2.99 ERA over the last two seasons for Oakland, completing a 50-game suspension for a positive testosterone test in between. The 40-year-old went 18-6 last season with a 2.65 ERA that was the AL's second-best mark, then signed a two-year, $20 million deal with New York this winter.
The right-hander's two strong seasons for the Athletics came after Gonzalez went 38-32 with a 3.93 ERA in his first four big-league seasons from 2008-11 for Oakland. Gonzalez was traded to Washington on Dec. 23, 2011, and has gone 32-16 with a 3.12 ERA in two years with the Nationals. He was 11-8 with a 3.36 ERA in 2013.
The only time these pitchers met was July 24, 2011. Colon allowed two runs over seven innings to earn a 7-5 victory for the New York Yankees, while Gonzalez was charged with six runs over 4 2-3 for the Athletics.
These starters figure to meet more this season, and Gonzalez could have the edge based on his history against the Mets. The left-hander is 5-0 with a 1.63 ERA in his last six starts versus New York, including 16 consecutive scoreless innings at Citi Field.
Colon has only faced three current hitters for Washington - Nate McLouth, Denard Span and Adam LaRoche.
Washington has won six straight over the Mets after opening this three-game set with a 9-7, 10-inning victory Monday. Anthony Rendon hit a three-run homer in the 10th inning and had a career-best four RBIs.
Span delivered a tying double with two outs in the ninth off Bobby Parnell before Rendon's home run helped give Matt Williams a victory in his managerial debut.
''That's what we want to have as our DNA - never give up, never give in," Williams said.
The Mets' new closer is likely to be veteran Jose Valverde after the team received the stunning news that Parnell has a partially torn elbow ligament after just 25 pitches this season and might need surgery. The right-hander, who missed the final two months of last season after neck surgery, complained of tightness in his elbow after Monday's game and an MRI revealed the tear.
David Wright went 3 for 5 with a two-run homer in the 10th for the Mets, who struck out 18 times and drew three walks.
''There's some things that we need to work on moving forward and that was pretty glaring in game one,'' he said.
Nationals star Bryce Harper was shaken up in the second inning when he got kicked in the forehead by second baseman Eric Young Jr. while breaking up a double play. Harper did not leave, passing concussion tests during and after the contest.
''I'm OK, but I've got a pretty bad headache right now," Harper said. "I was seeing stars there, but I've seen stars before.''
The Mets played Monday without Daniel Murphy and Chris Young. Murphy is expected back after he was with his wife for the birth of the couple's first child, while Young could return after he was out due to a mild right quadriceps strain.
Curtis Granderson hit cleanup and went 0 for 5 with three strikeouts in his Mets debut. He is 2 for 16 with a homer against Gonzalez.