Brendan Rodgers was particularly happy with his French striker pair Moussa Dembele and Odsonne Edouard, who were both on target.
The strong Celtic starting line-up saw them beat Shamrock Rovers 7-0.
This was Celtic's last game before the Champions League qualifying clash with Armenian side Alashkert.
The Celtic side will travel to Armenia with some extra confidence after such a successful match.
Rodgers gave his preferred starting lineup an hour on the pitch, before ringing in the changes to allow other players to get some game time in.
Celtic were already 5 goals up before Rodgers made the chunk of substitutions, with Edouard and McGregor both netting two and Dembele also scoring.
Substitutes Scott Sinclair and Lewis Morgan both added to the tally.
Celtic enjoyed the extra attacking power which the 3-5-2 formation gave them, with Dembele and Eduoard causing problems up the top.