His tweets, marked with #MillarTakeover, touched on topics ranging from his willingness to marry pitcher Ryan Dempster if he was a girl to Dustin Pedroia's exceptional defense at second base.
David Ortiz was also mentioned when he dropped off a special treat to Millar's children.
"Big Papi dropped off 4 suckers for my kids on way to on deck circle and said he was going deep #almost #MillarTakeover @KMillar15," the tweet read.
Ortiz's bid at a home run came up just short as he doubled off the wall in left field.
Millar currently works as an analyst for MLB Network where he is the co-host of "Intentional Talk."
He brought Jarrod Saltalamacchia on the show before the game Tuesday and talked in great detail about the catcher's hairstyle.
Millar apparently disappeared in the fifth inning.
"#RedSox lead 8-2 after 5. @KMillar15 has gone missing. He either went to find Pedro in the AC or is w/ the fam getting ice cream," a tweet from the Red Sox's account read.
But he returned shortly after as Boston pulled away to victory.
"10-4 @RedSox in the bottom of the 8th. Well this game looks good for the nation!!!! #MillarTakeover," the tweet said.
Michael Periatt is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.