Adelaide and Wellington played out a 2-2 draw in sauna-like conditions at Coopers Stadium that drew all-round criticism.
The barometer read 38 degrees just before kickoff at 4.30pm local time.
Phoenix asked for the game to be delayed but their request fell on deaf ears and assistant coach Chris Greenacre said later some of his players were ill with heatstroke at halftime despite drink breaks every 15 minutes.
"They're absolutely shattered," Greenacre said.
"It's about the welfare of the players, that is what matters. They are the guys out there that are really putting their necks on the line."
The A-League have a sophisticated 'wet globe' formula that determines the stress levels surrounding every match.
"All A-League matches are played under the FFA's heat policy, which is an agreed policy that offers a framework to ensure matches are played well within the world's best practice health and safety standards," an FFA spokesman said.
"The heat policy clearly states that drinks breaks should be implemented if the Wet Bulb Globe Temperature reaches 26 degrees and there should be consideration of delays and postponement if the WBGT reaches 28 degrees.
"The policy offers greater consideration to players' welfare than the FIFA policy and that of most other sports around the world.
"In line with FFA's heat policy both clubs were informed throughout the week of the forecast WBGT for Adelaide on Sunday to ensure the players were professionally prepared.
"The WBGT reading before the match on Sunday in Adelaide was 25.6 degrees.
"Despite this, A-League head Greg O'Rourke, who was at the match, consulted both team doctors and it was agreed to insert drinks breaks into the match as a further sign of FFA's interest in player welfare. This was all agreed and acknowledged by both teams.
"FFA has since been informed by medical staff at the match that no players suffered heatstroke during the match."
The A-League does not schedule Sunday matches beyond 5.30pm because the clubs feel that such kickoff times are late and make it hard for them to draw strong crowds.
Professional Footballers Australia have expressed concern over the events in Adelaide that also included an earlier women's league game between Adelaide and Sydney FC at the same venue.
Chief executive John Didulica said the players' union will monitor the players' health in the aftermath of the game.
"Following yesterday's matches in Adelaide, we have been in touch with all of our members and will continue to liaise with the clubs to monitor their health over the coming days," Didulica said.
"The professionalism of the players and the officials, in very difficult circumstances, was nothing short of remarkable and all of the feedback was that the players felt the pinch during the night and into the morning.
"Ultimately, whilst managing the fixtures is highly complex and the league is always looking to adopt best practice management, we need to have a greater emphasis on being flexible with our matches. Flexibility in scheduling safeguards the health of the players and the standard of the competition - two principles that should be non-negotiable.
"Two A-League matches on the weekend were impacted by either extreme heat or extreme travel, whilst Brisbane Roar are facing the prospect of five matches in 15 days and, in the process, travel more than 15,000km. Greater flexibility in scheduling ensures these variables are effectively managed in the interests of the players and the competition."
FFA said the wet globe reading was also 25.6 before the W-League match between Adelaide and Sydney that kicked off at 2pm.