Host Hanoi T&T beat Hoang Anh Gia Lai 2-0 at Hang Day Stadium on Wednesday in a match overshadowed by a controversial penalty.
With the win, the Hanoi club has secured a place in the semifinal round of the 2015 National Cup.
After defeating Cong An Nhan Dan 4-2 in penalty shootout in the previous round, Hoang Anh Gia Lai has strengthened its midfield area with Bui Tien Dung and Franklin Anzite.
Coach Guillaume Graechen said his players have received heavier training than when they were preparing for the Southeast Asian Games earlier this month.
A strong defense of tycoon Doan Nguyen Duc’s team has blocked all efforts of Hanoi T&T's Nigerian striker Hoang Vu Samson in the first half.
However, referee Tran Dinh Thinh awarded Hanoi T&T a penalty in the 42nd minute after Samson fell off while vying for the ball with Hoang Anh Gia Lai goalkeeper Minh Nhut.
Slow-motion images later showed that Minh Nhut did not touch Samson while trying to catch the ball.
Samson then had a successful penalty kick.
Hoang Anh Gia Lai’s efforts to level the score revealed dangerous gaps that were exploited by Hanoi T&T in the 83rd minute, when Samson had his second goal following an easy pass from Van Quyet.
In another quarterfinal match, host SHB Da Nang lost 1-2 to the National Cup's reigning champion Hai Phong, even though it was the first to score a goal.
A double by Jamaican striker Anthony Stevens secured Hai Phong’s ticket to the semifinal.
At Long An Stadium, host Dong Tam Long An defeated Dong Nai 4-2 in a match highlighted by a hat-trick by striker Tai Em.
In the rest quarterfinal match, Binh Duong beat host Song Lam Nghe An 2-1 at Vinh Stadium.
In two semifinal matches on August 5, Dong Tam Long An will play against Binh Duong and Hanoi T&T will play Hai Phong.
The final match is scheduled on September 26.