First Keane was to leave of his own accord, then he was to stay but retire from international football after the tournament.
Finally, when word broke of how he had criticised his manager and the Football Association of Ireland in media interviews, he was on his way home eight days before his side's tournament opener.
Roy Keane described the Republic of Ireland's training pitch as like playing on a carpark
Watson says he was "still finding his feet" in his new job after joining BBC NI but soon found himself thrust into a huge sporting story, one which the time difference ensured would play out across a virtual 24-hour news cycle.
"I didn't know as many of the Republic of Ireland players as I did the Northern Ireland players, so it was more a chance for me to try and get to know them," he recalls of the initial assignment.
"Relationships in my job are the most important thing. Building relationships with sporting stars is absolutely key, but as it turned out, having those relationships didn't actually matter when the Roy Keane story broke."
Watson admits he "took a gamble" to trust his instincts to stay behind when the Republic of Ireland team, and as a result the majority of the press pack, departed for Japan.
"My feeling was if Roy Keane's staying here, I'm staying here.
"There was the slightest opportunity that we could get some pictures of him, if we could get an interview with him even better.
"It was a long shot."
Roy Keane flew home eight days before Republic of Ireland's tournament opener against Cameroon
When Keane slipped out the back of what had been the team hotel to head for the airport and start his journey home, Watson and a few remaining photographers thought they had missed their chance but followed in a waiting van.
"There was a heightened tension within that van because we thought we'd missed him. Suddenly, very close to the airport, we saw [Keane] in a white van and we were euphoric," Watson remembers.
"Roy knew that he'd been rumbled and he jumped out of the van and then all hell broke loose I suppose. The flashbulbs went off left, right and centre.
"I said to the cameraman we need to go and ask some questions and I fired off four, five, six questions and [Keane] never changed his gaze, he never even looked at me."
As Keane waited in line for security, Watson tried again with the player's brief answers that followed the "gold dust" he had chased.
"It was a short interview but anything said by Roy Keane was going to be powerful," he adds.
Indeed it was with the quotes soon travelling far and wide.
The Keane saga cast a shadow of Republic of Ireland's tournament. Reportedly written on the wall of the team's dressing room as they reached the last 16 of the tournament...'no regrets'.
Watch 'Hold the Front Page: Roy Keane in Saipan' on Monday, 19 May at 22.40 BST on BBC One NI and BBC iPlayer.
