At the Tanimex tennis club in Tan Phu district on April 4, they won 6-2,7-5 in just over an hour and will next take on the winners of a matchbetween a Japanese and an Indian pair.
The win gives Quan and Khanh three points and a place in the ATP rankings, allowing them to play on the ATP Tour.
Carpenter said Quan and Khanh played better and deserved to win.
"[We were] not bad today but the Vietnamese duo played well," the 20-year-old said. "They combined well."
Quan faces Carpenter again in the last 16 of the singles today, and both men were confident.
"The chances are equal," Quan said.
Carpenter said: "It will be a tough game but I think I stand a good chance.-VNA