Lesotho defeated Mauritius 3-0 thanks to goals from Jane Thaba-Ntso, Jeremeka Kamela and Sera Motebang.
Kamela added to their lead from the penalty spot just before halftime, and then Motebang added the third late on.
The victory beats their previous record win in the COSAFA Castle Cup of 2-0 against Swaziland in 2013.
Mauritius were stung by the early goal and offered little going forward with Lesotho dominant throughout.
Angola’s side was made up largely of players in their Under-20 squad and they even included 15-year-old goalkeeper Eduardo Joao Bunga.
The youngster put in a fine display but could do little to stop the wave of Malawi attacks, led by Mhango.
It took 32 minutes for Malawi to open their account through the BidVest Wits-bound striker Mhango, before he added a second with a burst into the box 18 minutes from time.
He grabbed his hat-trick late on after Malawi were awarded a penalty, and they now move level with Lesotho at the top of the Group B standings.
Meanwhile, Monday could be pivotal in Group A as Zimbabwe desperately seek a victory to get their quarterfinal hopes on track.
They take on a slick-looking Madagascar at the Sam Nujoma Stadium at 19h30, seeking to overhaul the islanders in the table.
Zimbabwe were held to a 2-2 draw by Swaziland in their opener, while the Malagasy beat Seychelles 1-0 on Saturday.
Victory for Madagascar will see Zimbabwe eliminated, while a draw will also potentially take their own fate out of their hands.
Swaziland will expect to beat a Seychelles side that defended well against Madagascar but offered next to nothing going forward.
They have won both their previous COSAFA Castle Cup matches against the islanders, with that fixture to be played at 17h00.
Lesotho 3 (Thaba-Ntso 1’, Kamela 45’pen, Motebang 90’) Mauritius 0
Malawi 3 (Mhango 32’, 72, 90’pen) Angola 0
Swaziland vs Seychelles (KO 17h00 local, 16h00 GMT) – Sam Nujoma Stadium
Madagascar vs Zimbabwe (KO 19h30 local, 18h30 GMT) – Sam Nujoma Stadium
Matches Played: 4
Goals scored: 11
Biggest victory: Lesotho 3 Mauritius 0 (Group B, June 12); Malawi 3 Angola 0 (Group B, June 12)
Most goals in a game: 4 - Zimbabwe 2 Swaziland 2 (Group A, June 11)
3 goals – Gabadinho Mhango (Malawi)
2 – Felix Badenhorst (Swaziland)
1 – Claudel Fanomenza (Madagascar), Jeremea Kamela (Lesotho), Sera Motebang (Lesotho), Ronald Pfumbidzai (Zimbabwe), Obadiah Tarumbwa (Zimbabwe), Jane Thaba-Ntso (Lesotho)