"Pretty nervous to face that first ball, and then once I hit that I was set in. It was good batting out there."
Watkin reached her first 50 for New Zealand off 26 balls, having hit eight boundaries and two sixers.
She had been so zoned-in for the hunt to reach the Irish score of 136-8 that the personal milestone came as a surprise.
"It kinda snuck up on me pretty quick, so I didn't really know, and then Suzie gave me a handshake and I was like, 'oh, I better raise my bat now then'."
Wicketkeeper Bezuidenhout had a fine debut herself, getting five dismissals with the gloves – three catches and two stumpings – after Ireland won the toss and put themselves into bat.
The success will greatly improve Watkin's chances of establishing herself in the regular White Ferns playing XI as the tour moves onto three 50-over internationals with Ireland, followed by the T20 tri-series with South Africa and England, then three ODIs with England, the world champions of the format.