Natalya Coyle made a dream start to her third Olympic Games to occupy third spot in the modern pentathlon after the fencing round.
Coyle racked up 23 victories while suffering just 12 defeats to amass a total of 238 points.
Annika Schleu of Germany put in a remarkable performance to record 29 victories and six defeats to claim the early initiative at the Musashino Forest Sports Plaza, with South Korea's Kim Se-hee second after registering 24 victories and 11 defeats.
Coyle, who finished ninth overall at London 2012 and sixth at Rio 2016, returns to action at 6.48am Irish time in the 200m freestyle swimming event, with a second round of fencing, show jumping and an individual laser run concluding the competition later in the morning.
"I was really consistent and I'm absolutely buzzing after that," Coyle enthused when interview by RTÉ Sport.
"We've a good bit of rest now. Tomorrow I get to fence again and I'm really confident in my physicals. They've been really good and I've done some consistent training. I'm really looking forward to tomorrow."