O'Sullivan, one of the British and Irish Lions' "Saturday" coaches, who retakes the Ireland head coach reins for November's three Tests against Australia, New Zealand and Romania, is expecting a physical tour opener against the NPC side in Rotorua - exactly three weeks ahead of the first Test against Graham Henry's All-Blacks.
There may be none of New Zealand's five Super 12 outfits in action against the tourists over the coming weeks, but it's certain there will be no inch given by the Steamers, last season's Ranfurly Shield winners, tomorrow morning (8.10am Irish time).
"We will get hit very hard, very early. We have to be prepared mentally for that and not be shocked or surprised by it," said O'Sullivan.
"The one thing you can say about New Zealand rugby is that it is very physical, very aggressive and in your face. That is the first marker that is thrown down.
"I think discipline is very important and discipline let us down in Cardiff against Argentina. We kept giving away penalty opportunities and Argentina punished us," added the Corkman.
"I think that is a good marker for us for the tour. If we are sloppy with our discipline we will get punished. This is a very important game for us."
Captain Brian O'Driscoll added: "I'm sure Bay of Plenty will be very much up for the game. The opportunity doesn't come around for players who aren't in the international arena to play opposition like the Lions so I'm sure they will be chomping at the bit."
Bay of Plenty have played the Lions six times, losing five games and drawing 6-all back in 1966.