Beattie (16) hit the ball with ferocious power when it was in her zone and dominated the first set.
Scott (16) began to mix up the play and vary the angles and pace of her shots, and she put up more of a fight in the second set.
There was a score dispute early in the second set and Scott lost the replayed points, which proved vital.
If she could have held the second set, her movement and change of tactics might have paid dividends later.
Ryan Chow, a Canadian coaching in Wanaka, won the men's title.
He ran through the first set against titleholder Vaughan Kingi (Canterbury) 6-2, then had three match points in the second set tiebreak, but Kingi showed his desperation and high court speed to take the set at 9-7.
However, Kingi began to cramp and, after a medical time-out, he dropped the third set 2-6.
Earlier, Kingi reached the final with a hard-fought 6-4, 6-4 win over Jan Carboch, of the Czech Republic.
Chow had beaten Tyler Begg in the battle of the Canadians 6-4, 1-6, 7-5.
This match featured plenty of running as both players used all the court.
The women's semifinals were one sided, with Beattie dropping only two games against Louise Oxnevad (Queenstown), and Scott losing only one against Felicity Oxnevad.
In the third-place play-off, Louise Oxnevad beat Felicity Oxnevad 6-0, 6-0, and Sian English avenged an earlier loss at the Canterbury championships by beating Georgia Hume 6-1, 6-3 in the consolation final.
The men's consolation singles went to Julian Main (Canterbury), who beat Ryan Eggers (15) in the final after Eggers had upset experienced Otago representative Darryl Paterson in the semifinal.
Begg and Chow won the men's doubles final, beating Carboch and Mattias Wieland 6-3, 6-0.
Beattie and Scott won the women's doubles round-robin but were pushed to 6-4, 6-4 by Louise and Felicity Oxnevad.
