The Red Devils had defender Nathan Ngoy sent off for a last-man foul on Iran's Mehdi Taremi following a woeful back-pass on 66 minutes, but a stalemate remained and set up two crucial group finales.
Iran earlier thought they had taken the lead following a clever free-kick routine, but Taremi was deemed to be offside after a long video review.
Thibaut Courtois was also forced into two smart stops but otherwise Belgium dominated possession and chances, although they could not break through as Iran's defence put their bodies on the line.
In Belgium's 1-1 opener with Egypt, forward Romelu Lukaku had helped force the equaliser 22 seconds after climbing off the bench.
He was rewarded by Rudi Garcia with a start against Iran, his first for club Napoli or country since June last year following an injury-ravaged season.
But the 33-year-old and his fellow remaining veterans from the "Golden Generation" - who finished third in 2018 - looked short of ideas and need a win against New Zealand in the decider on Friday.
Lukaku told Sporza: "We had plenty of chances, but the ball just wouldn't go in. We need to analyse this match. We played with too much emotion. I'm pleased that I was able to play for over an hour, but of course not with the result. We have to win the next match."
Iran started the tournament with a 2-2 draw with New Zealand - in the same stadium in Inglewood, Los Angeles County.
For these two games, Iran had to travel from their Mexico base to the US less than a day before the game. For the group decider against Egypt in Seattle on Friday, they have been given more leeway.
The second consecutive draw leaves both Belgium and Iran on two points through two Group G matches. While each would still advance with a win on the final matchday on June 26, it leaves the door open for either New Zealand or Egypt to move atop the table should either win Sunday night's matchup in Vancouver.
Belgium face New Zealand in Vancouver on the final day of Group G play, while Iran simultaneously face Egypt in Seattle.
Iran's participation in the World Cup was shrouded in uncertainty in the build-up due to the war between the country and co-host the US.
There were boos for the Iranian national anthem from sections of the stadium used by NFL teams the Los Angeles Rams and Chargers.
The largest Iranian diaspora is present in southern California, many of whom are opposed to the government in the Islamic Republic, which heavily cracked down on opposition at home earlier this year.
Before kick-off, Iran said claims from Markwayne Mullin, the US homeland security secretary, that a person with ties to the Islamic Revolutionary Guard Corps (IRGC) tried to join the flight to the US on Saturday were "fabricated and entirely baseless allegations."
8°C