Niall McGinn gave the visitors a shock lead against the run of play after half-an-hour and, despite dominating possession, Portugal had to wait until the 80th minute for Helder Postiga to equalise.
Reflecting on a hugely impressive result that reinvigorates his side's World Cup campaign, O'Neill said: "I'm hugely proud of the effort and what the players gave us tonight. I think we saw a huge amount of character in this team."
He added: "It's a huge result. I don't tend to get carried away and the main thing for me is that regardless of the result, I was proud to stand there tonight and be their manager. That's because of what they gave to the cause and to each other."
The notion that O'Neill would leave Portugal frustrated at sharing the spoils seemed unthinkable before the match, but he admitted to a hint of regret having seen his side hold out for so long.
"We're very disappointed only to draw but we recognised that we would have to defend for our lives and that certainly proved to be the case, especially in the second half," he said.
"Having gone that far it was a bit of a blow (to concede). But we got what we deserved, simple as that, and I'm immensely proud of the players. There was nothing more I could ask from first to last."
O'Neill, whose side now have two points from their first three matches in Group F - including their two toughest away trips - declined to suggest how the result compared to other famous days in Northern Ireland's history.
Home wins over England and Spain in 2005 and 2006 remain the high watermark, but taming a side containing the likes of Cristiano Ronaldo, Nani and Joao Moutinho on their own patch will surely draw comparison.
"I'm sure it does, but that's for other people to say," O'Neill added. "I've told the players what I felt about their performance in the dressing room and that's all matters to me. It's up to other people where they want to rank that in history or in terms of benchmarking that performance."
Source: PA
Source: PA