After clawing their way back to 3-3 midway through the second half, fatigue set in and the hosts scored three more goals without reply.
''The girls played well for over an hour, but everything came home to roost in that game,'' said coach Ron Cane.
''The loss of key players to the squad, the injuries, the lack of game practise - we haven't played since we played Melville (on September 4) - and then that long travel up to Whangarei - all those factors put together meant we couldn't sustain the challenge.''
The standard of football was a step up for the Rotorua side.
''They were a good side - what was evident was that the league they play in is of a higher standard than the league that we play in," Cane said.
"But we got back to 3-3 and that was a magnificent effort from the girls. We were 2-0 down at halftime, then we got one back for 2-1. They scored again for 3-1 and we scored the next two.
"It was just hell for leather - they attacked us and we attacked them.''
But in the end, the defence just couldn't hold out.
''They had two very good strikers and at 4-3 I thought I'd be happy to go back to Rotorua with that. But that last part of the game, they just overwhelmed us," Cane said.
"We had players crawling from the pitch at the end. That told me that the girls had given everything.''
Rotorua's goal scorers were Kim Maguire, Hayley Merriman and Kieran Davidson.
Until he gets his players back together at training on Wednesday Cane is unsure which troops he will have on deck for the return match in Rotorua on Sunday.
''I've always got to be confident, but I also have to be realistic. There were some injuries and I don't know if they are going to get over them sufficiently to mount a good challenge.''
One positive will be the return of Maddi Ollington who has been away in Europe, but Cane will lose centre back Jordyn Ewert.
Cane said the three-goal lead Northland will take into the second leg is slightly flattering.
''But if the shoe was on the other foot, we would have taken advantage of a tiring defence. Now we've got to get back the three goals to start with.
"If the tie over the two legs finishes level, away goals will come into play, and Rotorua arguably have the advantage there with the three scored in Whangarei.
''It would be nice to do it, but I am realistic about our chances. If we put up a good showing and if we win the game that would be a good bonus.
"Even if we don't qualify for Northern League selection, if the girls can, for one last time this season, drag themselves up to put on a good show, then I'd be more than happy with that.''
Lotto NRFL playoff series second leg
Sunday 25 September: Rotorua United v Northland Football Club, Neil Hunt Park, Rotorua.
