In his last three starts, Hammel is 2-1 with a 2.21 ERA while opponents are hitting .218 off him.
"He's really settled in," Royals manager Ned Yost said. "He really looks good right now."
Velazquez, 28, was signed this spring out of the Mexican League. He made one start on May 18 and gave up nine hits and six runs in an 8-3 loss to Oakland. Since then, he has made one relief appearance -- 3 1/3 shutout innings against the Phillies. Velazquez posted a 1.29 ERA in nine starts at Triple-A Pawtucket.
"We're going to be going up against a team that is playing extremely well and they're swinging a lot of hot bats," Red Sox manager John Farrell said. "So location will always be the key, particularly against a team that's swinging the bat like they are."
Things to know about this game
• Hammel will have to be careful with Red Sox designated hitter Hanley Ramirez and second baseman Dustin Pedroia. Ramirez is hitting .462 against Hammel with a double and a home run, while Pedroia is hitting .364, also with a double and a home run.
• The Red Sox haven't faced Hammel since 2013. He has a 4.61 career ERA against the Red Sox in 13 career outings.
• Lorenzo Cain has gone from having one home run on the season on the morning of May 23 to having 10 midway through June, and one of the Majors' hottest hitters has turned around his contact metrics this month. Cain's rate of "productive" contact (or the three batted ball types -- barrels, flares/burners and other solid contact -- that Statcast deems most favorable to the hitter), barrel count (from three combined in April/May to seven this month) and average exit velocity (88.5 mph in April/May to 91.7 mph in June) have all jumped up as the weather has gotten warmer.
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.