March 30, 2017 0823 GMT
The Pacific Ocean islanders made a stunning start to the qualifiers with home wins over Turkmenistan and India before Thursday's meeting with Asia's top-ranked side, but Iran at Tehran's Azadi Stadium proved too strong for Matao, with the three-time Asian champion cruising to a 4-0 lead at the halftime interval, the-afc.com reported.
Iran was given a golden opportunity to take a 10th minute lead when referee Khamis al-Marri awarded the home side a penalty, which was successfully converted by Ashkan Dejagah before Persepolis forward Mehdi Taremi doubled the advantage just after the half-hour mark.
Russia-based Sardar Azmoun, who scored three times at the 2015 AFC Asian Cup back in January, continued his prolific form for Carlos Queiroz's side with goals in the 34th and 41st minutes as Iran all but sealed the three points by halftime.
Guam showed more resilience after the restart but was breached for a fifth time when Taremi scored his second of the match before Saipa winger Mehdi Torabi sealed the 6-0 win in the last minute.
Iran will head to Bangalore to face India on Tuesday, with Stephen Constantine’s side seeking its first point(s) of the campaign following back-to-back defeats, while Guam will be hoping that its home form will see the team return to winning ways when it will entertain Oman on the same day.
The group winner and four best runner-up (total 12 teams) will advance to the 2019 AFC Asian Cup finals and the final round of qualifying for the 2018 FIFA World Cup.
The next best 24 teams from the preliminary stage of the joint qualifiers will compete in a separate competition for the remaining slots (12 slots or 11 slots + 1 slot for the host) in the 24-team 2019 Asian Cup.
Iran has collected 716 points to stand ahead among the Asian teams, according to the latest football world rankings released by FIFA.
South Korea and Japan are behind Iran in the monthly rankings, AP reported.
World Cup winner Germany dropped to No. 3 in the latest FIFA rankings, with beaten finalist Argentina still at No. 1.
Germany trades places with new No. 2 Belgium as its World Cup results drop in value more than one year later.
The Netherlands fell seven places to No. 12, also because its third-place finish in Brazil counts for less in FIFA's calculations over a four-year cycle.
Colombia stays at No. 4, and Brazil and Portugal each rise one to No. 5 and no. 6, respectively.
Copa America winner Chile climbs one to No. 10.