Qatar thrashed Maldives 4-0 in Doha to record their fifth straight win in the qualifiers to enjoy a five-point cushion ahead of Hong Kong in Group C.
In Hanoi, Thailand trounced South-East Asian rivals Vietnam 3-0 in front of 35,000 spectators in Goup F.
Enjoying a rare unbeaten spell under Uruguayan coach Jose Daniel Carreno, Qatar struck twice through Boualem Khoukhi, while Mohamed Kasola and Mohamed Musa completed the tally.
It was Qatarâs second home victory in less than a week, after beating rivals China 1-0 in the same Al Sadd stadium 1-0 and they now look set to make the next round with some degree of ease.
In Hanoi, a first-half strike by Kroekrit Thawikan put the visitors ahead at My Dinh Stadium before an own goal by Dien Tien Thanh and an effort by captain Theerathon Bunmathan sealed a comprehensive win for the visitors who moved five points clear of Iraq at the top of their group.
Thailand had needed a late goal to beat Vietnam 1-0 in Bangkok in May but Kiatisuk Senamuangâs side were in top form in Hanoi and took a deserved lead in the 29th minute when Kroekrit unleashed a 25-metre drive with his left foot into the top corner of Tran Nguyen Manhâs net.
In Group B, giantkillers Jordan consolidated their position at the top with a 3-0 rout of Tajikistan. Hamza al-Daradreh, who had scored a pivotal role in Jordanâs upset of Australia last week, was once again the hero with two goals while Hassan Abdel Fattah completed the tally.
War-torn Syria also boosted their chances of qualifying with a 5-2 win over Afghanistan in Muscat which took their tally to 12 from five matches in group E.
North Korea also boosted their hopes of advancing to the next round after a 1-0 home win over Yemen while Singapore and Hong Kong claimed narrow wins against Cambodia and Bhutan respectively.
North Korea consolidated their position at the top of Group H with a narrow home win over last-placed Yemen in Pyongyang.
Jong Il-gwanâs 12th minute penalty proved decisive at Kim Il-sung Stadium as the Chollima moved four points ahead of second-placed Uzbekistan, who have played a game less.
Hong Kong moved up to 10 points in Group C, two points behind leaders Qatar, after edging a gallant Bhutan 1-0 in Thimphu. The home side had looked set to earn their first point in the group until Chan Siu Ki grabbed the winner for the visitors a minute from time.
Cambodia also remained pointless in Group E after they lost 2-1 at Singapore.
The home side took the lead through Faris Ramli after 16 minutes and after Khairul Amri had missed a penalty late in the first half, they extended their advantage when substituted Fazrul Nawaz capitalised on a defensive error two minutes after the interval.
Sos Suhana narrowed the deficit midway through the second half but the Indochinese side were unable to find an equaliser as they suffered their first straight defeat in the group.
Meanwhile, Malaysia and Laos moved off the bottom of their groups after picking up the first wins of their campaign.
Malaysia won 1-0 at Timor Leste in Group A with a 10th minute strike by Amri Yahyah while Myanmar came from a goal down to beat Laos 3-1 in Group G.
The winners of the eight second-round groups and the four best-performing runners-up will advance to the next round and also earn berths at the 2019 AFC Asian Cup in the United Arab Emirates.