The first goal allowed under the experimental "daylight offiside" law was scored in Canada on Saturday when Pacific FC forward Alejandro Diaz's strike against Halifax Wanderers was permitted by officials.
FIFA's proposal to change the offside law in favour of the attacking team started trials in the Canadian Premier League earlier this month after failing to win support from European football officials.
The so-called "daylight offside" idea pushed by Arsene Wenger in recent years gives a big advantage to attackers -- too much, according to critics who say it will force teams to drop back and defend more cautiously.
The law judges attackers to be onside if any part of their body that can score a goal is level with the relevant defender. In effect, offside is called only when there is clear daylight between the attacker and defender.
Alejandro Diaz's goal would have been ruled out by leagues following the standard International Football Association Board (IFAB) Laws of the Game. However, it was allowed to stand under the Canadian league's ongoing trial conducted in cooperation with FIFA.
The current offiside law being applied in most competitions sees attackers judged offside by a slew of cameras in the stadium for extremely small margins, often derisively called "armpit" or "toenail" offsides by fans.
The Premier League, which uses semi-automated offside technology, allows a tolerance level, or benefit of the doubt, of about 5 centimetres to their offside calls, allowing goals such as that scored by Liverpool's Florian Wirtz against Fulham in January to stand despite replays appearing to show him being in a marginally offside position before finding the back of the net.
If the trial in Canada is deemed to be a success and proves popular, Wenger's daylight plan can be written into The Laws of The Game if voted for by at least two of the four British federations who sit with FIFA officials at the annual IFAB meeting.
Information from the Associated Press contributed to this story.