Goals in the first half from Pablo Rosario and Denzel Dumfries put PSV in control before the break but Groningen hit back through Ramon Lundqvist to give them a chance late on.
Bruma’s injury-time strike made sure PSV would take all three points but Van Bommel wasn’t happy with what he saw from his side the longer the game went on.
Reflecting on the first half, he said: “We were dominant in the first half and put in a fine display. We were fully focused, dominated possession and played some good football.”
However, it was a different story for him after the interval as he hit out at his side’s sloppiness.
He added: “We frequently lost possession and made it hard for ourselves. Ramon Lundqvist pulled a goal back, but we scored a late goal to put the result beyond doubt. I am happy to have bagged all three points.”
PSV sit second in the Eredivisie after seven games, level on points with leaders Ajax, while Groningen are down in 14th.
Next up for PSV is a trip to PEC Zwolle on Sunday.