The striker is a huge golf fan, and was frequently pictured with club in hand during his five-month exile from Manchester City last season.
However, his major caddying debut did not go to plan, as Romero shot a 12-over-par 82, one of the worst rounds of the week, leaving him dead last of all the players to make the cut.
Romero, who was already well off the pace, teed off at 8am alongside Chad Campbell, and he and Tevez quickly found trouble, dropping five shots in the first four holes.
The 31-year-old carded just a single birdie on the 11th, and double-bogeyed four times.
Tevez nonetheless declared himself delighted, saying: "I enjoyed the round. The course is beautiful. The chance to walk along the course and to be around these great players is a pleasure and something unforgettable.
"This is the dream of everybody who plays golf. It was my first major!
"It was difficult to carry the bag because it weighed so much but it was fine." Tevez said.
"I couldn't give any advice about the slopes but I just carried the bag and supported him each hole. Romero is a professional and he knows everything already. We worked together very well."
Romero, who finished third behind Padraig Harrington and Sergio Garcia in the 2007 Open at Carnoustie, added: "We all agreed Carlos would take the bag today and we really enjoyed the moment.
"He did not complain at all when I asked him if he was in any pain. I played really badly today but he was helping me with my confidence."
Tevez's trips to the golf course became infamous last season when he went AWOL from City.
On scoring against Norwich City after returning to the club in April, the 28-year-old celebrated with a golf swing.
City begin their Premier League title defence in less than four weeks.