So into a playoff they went and on the second extra hole separation was finally made as Harrington ran home a birdie putt and then watched in disbelief as Romero missed from just three feet for his birdie.
Harrington nevertheless welcomed the win as he got his first victory in a playoff after having a career 0-3 record.
'I felt sorry for Eduardo missing there on 18 and here (No. 2), but I wanted it badly,' said Harrington, who trounced Mark Calcavecchia in their singles match last week at The Belfry. 'I thought Eduardo played great too. It's a shame that somebody had to lose in the playoff. I've been there before.'
It was Harrington's first win of the season and vaulted him into contention for the top spot on the European Order of Merit (money list). The $808,000 first-place check puts him within striking distance of Retief Goosen and Ernie Els.
Harrington almost didn't get into the playoff, save for a clutch putt on the event's last hole.
Needing birdie to match Romero's score of 19-under, the Irishman hit a wedge to 15 feet and then saw Romero do him one better as Romero his wedge to about six feet.
Fittingly, the duo had swapped the lead througout the tournament and came into the final round tied. Harrington ran home the putt for birdie on 18, and waited for Romero, who had a chance to end it in regulation.
A little shell-shocked after watching Harrington's ball drop into the cup, Romero proceeded to pull his six-footer for the title and thus set up the playoff.
After both had routine pars on the first extra hole, they each found the fairway on the second playoff hole. Harrington hit first and played a beautiful wedge to 16 feet.
Romero again topped Harrington as his wedge nestled up to about three feet from the cup.
And just like the 18th in regulation, Harrington was up to the task and drilled what turned out to be the winning putt.
Romero, who had played brilliantly all week, couldn't convert the small tester to extend the match. It would have been his second win of the season.
'I think that it was more my fault,' said the 48-year-old Romero, who lost out on his bid to become the oldest winner in European Tour history. 'I make mistakes and I don't putt too good at the last two holes. Especially on the last one. I putted from three feet for birdie.
'But I'm very happy. My game is very good. Very solid. I concentrate and my putting is working. I'm very happy.'
Colin Montgomerie tried to steal the show with an amazing 9-under-par 63 that included a string of birdies on the 7th, 8th, 9th, 10th, 11th and 12th holes. A bogey at the last hole left him in a tie for third with Vijay Singh and 1988 Masters' champion Sandy Lyle.
Final scores from the Dunhill Links Championship