Just after the explosions, Arredondo lifted the severely wounded Bauman into a wheelchair and found help.
When Bauman, who was at the race to cheer on his girlfriend, awoke from surgery, he helped the FBI identify the alleged suspects in the attack.
On Tuesday, Bauman and Arredondo chatted with Red Sox legend Pedro Martinez before taking the mound. As the stadium announcer told their story, the crowd rose to its feet and roared.
Bauman and Arredondo, who was wearing his cowboy hat, pointed at each other and gave a thumbs up before throwing a pair of strikes to David Ortiz and Jarrod Saltalamacchia.
Michael Periatt is an associate reporter for MLB.com. Follow him on Twitter @Michael Periatt. This story was not subject to the approval of Major League Baseball or its clubs.