Kuwait also had an easy outing in the day's other Group B match as they beat Thailand 3-1 in Bangkok.
Naif Hazazi came off the bench to score a second-half winner for three-times champions Saudi Arabia in their clash at home against Jose Antonio Camacho-coached China.
In another Group C match, Iraq dominated against a defensive Indonesia at the neutral Al Rashid Stadium in Dubai but had to be content with a 1-0 victory.
The top two teams from each of the five qualifying groups and the best third-placed team will join defending champions Japan, hosts Australia, South Korea and North Korea in March 2015 for the next edition of the tournament.
Nekonam converted two penalties and added Iran's fifth and final goal while Standard Liege striker Reza Ghoochannejhad scored a brace to exact sweet revenge for the hosts' 1-0 loss to Lebanon last September in Beirut in a World Cup qualifier.
Coach Carlos Queiroz felt the margin of the win will boost the morale of the players who were under pressure having lost at home to Uzbekistan in November in another World Cup qualifier.
"I appreciate the effort from my players, they kept fighting and never gave up," the former Portugal and Real Madrid coach was quoted as saying by the AFC website (www.the-afc.com).
"We were able to highlight the gap between Iranian and Lebanese football.
"After we lost at home to Uzbekistan we needed to do something to relieve the pressure and we were able to beat Lebanon 5-0 which will alleviate the negative atmosphere."
In Group A, Jordan eased past hapless Singapore 4-0 at home while Oman had to dig deep to beat Syria 1-0 at home in Muscat.
Both Bahrain and Qatar scored twice in the second half to win their Group D matches by identical 2-0 margins against Yemen and Malaysia respectively.
In Group E, the United Arab Emirates carved out a 2-1 win over a fighting Vietnam side while Hong Kong, who played the last 30 minutes with 10 men, defended heroically to hold Uzbekistan 0-0 in Tashkent.
"I am satisfied with the result. We were unable to achieve a victory, but we achieved a good result," Hong Kong coach Kim Pan-gon said.
"I think we deserved the result. We had a little luck as they hit the crossbar, but we played good football even though we had a player sent off in the second half."
Out-of-form Saudi Arabia, who last month sacked coach Frank Rijkaard after the team failed to make it past the group stage of the Gulf Cup of Nations, got the much-needed win after Hazazi turned in a cross from Al Ittihad team mate Al Muwallad.
Fahad Al Muwallad had opened the scoring for the hosts, who have also failed to qualify for the 2014 World Cup, but Zhao Xuri restored parity for China before the break.