Evans Rusike was also on target as Sunday Chidzambwa’s side had too much quality for the islanders and should have won by a greater margin.
Lesotho also sealed their Last 4 place with a penalty shoot-out victory over Uganda after those two sides played to a 0-0 draw.
Comoros and Uganda now drop into the Plate competition, with those semi-finals being played on Tuesday.
Zimbabwe picked a strong side and also had Belgium-based striker Knowledge Musona come off the bench as they sent an ominous message to the rest of the field as to their prowess in this year’s competition.
Zimbabwe were ahead inside five minutes and it was a simple score. Defender Tendayi sent an inviting ball into the Comoros box and Rusike headed past a stranded Fahadi Mohamed in the islanders’ goal.
Billiat provided a superb touch to make it 2-0 on 36 minutes, meeting the floated pass from Rusike on the volley and steering is expertly past Mohamed.
Having missed two good chances earlier, it was a sweet moment for the Kaizer Chiefs forward.
Billiat should have got a second when Darikwa’s delightful low cross was put on a plate for the striker, but he missed the ball altogether from four yards out.
Rusike forced an excellent save from Mohamed early in the second period as Zimbabwe continued to press, but they could not add to their tally on the night.
Lesotho sealed their deserved triumph in a shoot-out, when Uganda only managed to convert two of their five spot-kicks, asJohn Revita and Paul Mucureezi saw their efforts saved, and Mustafa Kizza missed altogether.
Crocodiles goalkeeper Samuel Khetsekile had an excellent game and was deservedly named Man of the Match, making a number of important saves in the 90 minutes as well.
Michael Birungi misses three good chances for Uganda early on as they enjoyed the ascendency, but the longer the game went on, Lesotho gained the ascendency.
Motebang Sera’s flick into the path of Tsoarelo Bereng saw the latter crash the ball against the post, while at the other end Khetsekile tipped Muzeyi Serunkuma’s effort onto the woodwork.
Lesotho had the ball in the back of the net through Sera, but goal was wrongly ruled out for offside, and late on he scored again, though this time the assistant referee got the offside call right.
That sent the match to penalties and Lesotho always looked the more confident from 12-yards and were clinical from the spot.
The final two quarterfinals will be played on Sunday at the same venue as South Africa play Botswana (kick-off 15h00 local; 13h00 GMT) for the fifth year in a row in their opening fixture.
Botswana have never beaten South Africa in 90 minutes in 14 previous attempts, but come up against an untested, largely Under-23 line-up from the hosts.
South Africa have also been dealt a double-blow with the loss of Phakamani Mahlambi and Keagan Dolly this week, and are led by coach David Notoane.
The last of the quarterfinals sees Zambia, beaten finalists in the last two editions, take on Malawi (17h30 local; 15h30 GMT), who have shone in the competition so far having come through the pool stages unbeaten.
Malawi have a young squad at the COSAFA Cup, but are full of youthful exuberance and no shortage of skill, and will be a big test for a home-based Zambian squad.
Lesotho 0 Uganda 0 – Lesotho won 3-2 on penalties
Zimbabwe 2 (Rusike 5’, Billiat 36’) Comoros 0
South Africa vs Botswana (KO 15h00; 13h00 GMT) – Princess Magogo Stadium
Zambia vs Malawi (KO 17h30; 15h30 GMT) – Princess Magogo Stadium
Group A P W D L GF GA Pts
Comoros (Q) 2 1 1 0 4 3 4
Eswatini 2 0 2 0 4 4 2
Mauritius 2 0 1 1 3 4 1
Group B P W D L GF GA Pts
Malawi (Q) 3 2 1 0 6 2 7
Namibia 3 2 0 1 6 3 6
Mozambique 3 0 2 1 2 3 2
Seychelles 3 0 1 2 0 6 1
Matches Played: 11
Goals scored: 27
Biggest victory: Malawi 3 Seychelles 0 (Group B, May 26)
Most goals in a game: 4 – Eswatini 2 Mauritius 2 (Group A, May 25); Eswatini 2 Comoros 2 (Group A, May 27)
3 goals – Ashley Nazira (Mauritius)
2 – Felix Badenhorst (Eswatini), Issaskar Gurirab (Namibia), Youssouf Ibroihim (Comoros), Gabadinho Mhango (Malawi), Gerald Phiri Jnr (Malawi)
1 – Khama Billiat (Zimbabwe),Charles Hambira (Namibia),Soulaimana Ibouniyamine (Comoros), Jeituso (Mozambique), Hassan Kajoke (Malawi), Absalom Iimbondi (Namibia), Joslin Kamatuka (Namibia), Siboniso Mamba (Eswatini), Richard Mbulu (Malawi), Sabelo Ndzinisa (Eswatini), Boina Bacar Raidou (Comoros), Evans Rusike (Zimbabwe), Sadney Urikhob (Namibia), Witi (Mozambique)