Laura Robson battled to victory against Heather Watson in the first meeting between the British teenagers at the Aegon GB Pro-Series Barnstaple.
Londoner Robson, 17, fought out a 6-1 3-6 6-3 win over Guernsey 19-year-old Watson to reach the quarter-finals.
It was an impressive result for Robson, ranked 48 places lower at 135.
"I'm sure we're going play a fair few times in the future and we're friends, so it was always going to be a tough match," Robson said.
"It happens all the time on tour [that friends play each other] so you've just got to deal with it as best you can.
"It's hard to say [how far she and Watson can go]. Heather has improved so much over the last year-and-a-half, she's really consistent now.
"We'll both work as hard as we can but I don't want to talk about numbers or expectations as that will only add pressure. As long as we work really hard, we can do well."
Robson and Watson were together on court later but lost their doubles match 6-4 2-6 11-9 to fourth seeds Maria Joao Koehler of Portugal and Hungary's Katalin Marosi.
British number three Anne Keothavong overcame American veteran Jill Craybas 6-2 6-0, but there were defeats for her compatriots Naomi Broady and Tara Moore.
Broady, Britain's number five, pushed world number 169 Ekaterina Bychkova to three sets but eventually succumbed 6-3 6-7 (4-7) 6-4 as the Russian advanced to a last-eight match against Robson.
Moore, ranked ninth in Britain, lost 7-6 (8-6) 6-3 to Portugal's Maria Joao Koehler.
British number one Elena Baltacha is absent from the competition as she opts to ends her season at the ITF event in Poitiers, France.
The Barnstaple tournament is part of the second-tier ITF circuit, giving players the chance to pick up points late in the year as the WTA season comes to an end.
The meeting between young British hopes Robson and Watson brought added interest to the competition, and it was 2008 junior Wimbledon winner Robson who coped better with the pressure.
After the opening two games went with serve, Robson took charge with back-to-back breaks of serve as she raced through the first set.
The left-hander continued her charge with another break at the start of the second and made it seven games in a row as she moved 2-0 clear.
Watson, who won the US Open girls' title in 2009, finally grabbed a foothold in the match by breaking for the first time to make it 2-2 and got the crucial break at 4-3 before levelling at one set all.
The decider was a tight affair and it was Robson who made the decisive move to go 4-2 up, and she held her nerve to serve it out at the first attempt.