The arrival of the trio on the final day of the transfer window comes after the signing of FC Seoul's Ki Sung-Yong, Thomas Rogne from Stabaek, Brondby's Morten Rasmussen and Jos Hooiveld from AIK Stockholm.
With just over one minute on the clock, Celtic opened the scoring when Ki Sung-Yong delivered a low free kick back into the St Johnstone penalty area from wide on the right and Stokes fired in from 18 yards.