Diogo Jota scored twice in the first half to earn Portugal to 2-0 lead against Serbia in Beograd but the hosts fought back after half-time.
Serbia’s all-time top scorer Aleksandar Mitrovic pulled one back in the 46th minute, before Filip Kostic leveled on a break on the hour.
There was late drama after Nikola Milenkovic’s red card when Portugal thought they’d scored a winner from Cristiano Ronaldo’s effort where Stefan Mitrovic desperately tried to clear it off the line.
Replays suggested the entire ball had crossed the line but the linesman did not flag to award the goal, leaving Ronaldo and his teammates raging. There is no VAR in World Cup qualifying.
Ronaldo led the remonstrations, charging at the linesman, earning a yellow card and storming off the pitch.
“In a match of this level, that isn’t possible,” Ronaldo later posted on Instagram: “I always give and will give everything for my country, that will never change.
“But there are difficult times to deal with, especially when we feel that an entire nation is being harmed.”
Elsewhere in the group, Republic of Ireland slumped to a dismal 1-0 home defeat to Luxembourg, who are ranked 98th in the world.
Belgium were held to a 1-1 draw by Czech Republic with Romelu Lukaku equalising, while Croatia edged Cyprus 1-0 with Mario Pasalic netting the winner.
Despite possessing some star names, Norway were also humbled 3-0 at home by Turkey, while the Netherlands got past Latvia 2-0.