Thornburg is at last over the right shoulder woes that plagued him even long before he had a procedure to repair Thoracic outlet syndrome last June.
"It's just been one of those that at times it's felt like it was never going to get here and then other times it felt like it was right around the corner and kept going and going so, yeah, I feel like I've been waiting long enough so I'm definitely excited," Thornburg said.
To make room for Thornburg on the 25-man roster, the Red Sox optioned right-hander William Cuevas to Triple-A Pawtucket after Tuesday's 11-4 win.
Initially acquired to be Craig Kimbrel's primary setup man, Thornburg will have a lower-leverage role to start as he gets back up to speed.
The Red Sox will probably be conservative with his workload in the beginning.
"It's going to be something where I'm going to have to stay on it and be smart about, but the good part is as the season progresses it should be something that just continues to tick up the more outings I get," Thornburg said.