And the second of Guinan's goals was set up by youngster Sam Gwynne, who snapped up the third himself to notch his first goal for Hereford and round off a comfortable victory.
The Bulls took the lead with just 15 minutes played. A cross from Kris Taylor was only partially cleared by Drissa Diallo and Guinan was quickly on to the ball to rifle a shot past goalkeeper Shane Higgs.
The keeper produced an excellent save to keep out a drive from Andy Williams on 24 minutes, but only delayed the second goal by a matter of two minutes.
Gwynne won the ball from Darren Kenton on the Hereford right and slipped a quick pass to Guinan, who controlled the ball before smashing a right-foot shot past Higgs from 15 yards.
Hereford's on-loan keeper Matt Murray pulled off a good save from Scott Murray as Cheltenham attempted to hit back and then Dean Beckwith block tackled Lloyd Owusu as Town threatened again.
Two minutes into the second period, Guinan raced on to another neat pass from Gwynne, but this time drove his shot just the wrong side of an upright.
Gwynne's own moment of glory, however, arrived 11 minutes into the half. Higgs was indecisive as Murray booted a long goal-kick downfield and Gwynne nipped in to slide the ball into an empty net.
His enthusiastic goal celebrations cost him a yellow card.
As was to be expected, Cheltenham, who had used all three substitutes at the interval, piled everything forward in search of a consolation.
But the closest they came was in the 71st minute when a long-range drive from Paul Connor finally beat the immaculate Murray, but came back off the post.