Boyd has re-joined Killie until the end of the season after leaving MLS side Portland Timbers.
And Shiels believes the effect of the SPL's all-time top scorer with 164 goals was felt at the club before he has even stepped on the pitch.
"The signing had an effect on today as (Paul) Heffernan and (Jamie) Langfield were outstanding," said Shiels.
"He's made a major contribution to this club and is a legend here - it's great to have a player like that here.
"Aberdeen have quality right through their team, I think after they enjoyed the better of the first 20 minutes and hit the post, that could have killed it off. But we dug in, made some chances and then got the goal we deserved.
"The first 20 minutes of the second half we were bossing it and then Aberdeen started hitting us on the break."
Shiels' opposite number, Craig Brown, was incensed by referee Euan Norris' decision not to award a penalty and send off Killie goalkeeper Cammy Bell when he brought down Niall McGinn 10 minutes from time.
However, Shiels offered a diplomatic answer when quizzed on the incident.
He said: "If I talk about referees and penalties then I could be penalised - I'm going through a self-discipline programme at the moment to try to stay away from the truth as much as I can."