And while many Lions would have seen selection for a Tuesday-night fixture immediately prior to the first international as a indication that they would being missing out the following Saturday, O'Callaghan says he still believed he had a shot at a Test place and felt nothing but pride at being asked to skipper the world's most-famous touring side.
"I didn't expect the captaincy at all," said O'Callaghan told the Irish Examiner.
"I was delighted although it was a big surprise. Still, it was a tough game to motivate the lads for, and as much as the management was saying that the Test team wouldn't be picked until the Wednesday, I don't think a lot of the lads believed that.
"Personally, I was probably the only one who thought it on that Tuesday match. Mike Blair slagged me over it. He was there saying, 'hold on a second, you thought you were going to play Saturday, Tuesday and Saturday', and he burst out laughing! 'You're mental, Dunners'!
"I took the coaches at their word, and I've no doubt they didn't pick that Test team until the Wednesday but I wasn't able to force my way into it."
Although he clearly enjoyed the honour of captaining the midweek Lions, not being able to play a greater role in the three-match Test series against the Springboks was a major disappointment for the 30-year-old lock forward.
Selected as a replacement for the first international in Durban, O'Callaghan missed out to O'Connell, Simon Shaw and Alun-Wyn Jones in Pretoria and Johannesburg. Now back in training with Magners League winners Munster and Grand Slam winners Ireland, O'Callaghan knows that the best way to get over that disappointment is to continue to impress with province and country.
"Of course I was disappointed not to get in the Test team," added O'Callaghan, who appeared in all three internationals when the Lions toured New Zealand four years ago.
"I went out there to get in the Test team and didn't. I wasn't the only one - there were 36 of us out there and anyone who didn't get in the Test team was disappointed so I was no different.
"I went out there saying that I would give it everything and I think I could come away saying I did. It didn't go my way, I suppose, and the best thing at this stage when you come away from something like that is looking to prove people wrong...I've never been more motivated for a season."