Oakland won five straight over Cleveland and Tampa Bay to begin this trip, but lost an 11-inning finale to the Rays on Thursday before being swept by the Blue Jays for the first time since 2008.
“When you win the first five it’s pretty disappointing to lose the next four,” Melvin said.
The long game Thursday let to a late arrival in Toronto, where three more games on an artificial surface took a further toll.
“I think some of us are just a little worn down from the last six games on turf,” Oakland catcher Derek Norris said.
The Blue Jays, who lead the AL East, won their season-best sixth straight. It’s Toronto’s longest streak since an 11-game run last June. The Blue Jays have won 11 of 13 and 16 of 21.
“We caught them when they were hot and they handed it to us,” Melvin said.
Encarnacion hit a one-out drive into the second deck off Athletics left-hander Drew Pomeranz in the fourth. The homer was Encarnacion’s 12th this month, tying the team record for May set by Jose Bautista in 2010.
The Blue Jays record for home runs in a month is 14, set by Bautista in June, 2012.
Encarnacion’s 14 home runs this season are tied for third most in the majors. Only Baltimore’s Nelson Cruz (16) and Chicago White Sox Jose Abreu (15) have hit more.