Now he wants another look at him this weekend to see if 33-year-old talisman can maintain the inspirational form that earned him the man of the match award last weekend.
Speaking about O'Connell's performance last Sunday, Gatland told Sky Sports' Rugby Club: "He was one that definitely caught the eye. He was good, but that's what you expect of professional athletes and players that have been at the top of the game for a long time.
"You expect that when they come back they make an impact and difference. He did that, but it's about us not getting carried away - it's only one game.
"He definitely took the eye of a number of people including ourselves, particularly at line out time, around the field and his leadership qualities. I've a huge amount of time for Paul and all he has achieved.
"His successes have been with Munster and Ireland but probably if he looks back on his career he'd love to go on another Lions tour and get win a series in the Southern Hemisphere. It's something not a lot of players have achieved.
"It will be interesting to see how he goes over the next couple of weeks and we will go to watch him again this weekend. Hopefully, that form will continue this weekend."
Odds on O'Connell being the Lions captain again have shortened remarkably since his Heineken Cup comeback and he is now the favourite with a number of bookies. But Gatland is keeping his cards close to his chest on that score.
"I'm pretty clear on who I would like to do it, but I haven't spoken to that person.. Every player has probably been asked has Warren Gatland spoken to you, so I will probably leave it as late as possible," admitted Gatland.
"I'd like to make sure when the squads announced it's something special. I don't want it to be leaked and ideally I'd like to keep the captaincy quiet as well. It's going to be hard but that's the plan."