The FIA has admitted "human error" caused a power disparity during Sprint Qualifying in Singapore.

Following a red flag for debris in SQ1 caused by Cadillac's Sergio Perez, the FIA did not activate Overtake Mode - an extra power boost that is normally active throughout qualifying and used in races to aid overtaking.

The FIA reactivated Overtake Mode for 27 seconds before deactivating it again, thus causing an unfair advantage in the first part of Sprint Qualifying.

Sky Sports F1 understands the brief re-activation of Overtake Mode happened in the last minute of SQ1 when several drivers were on flying laps before being turned off.

Williams' Carlos Sainz was one of the six drivers to miss out on SQ2 and says the drivers who had Overtake Mode for those 27 seconds gained around half a second.

There was also a timing issue during Sprint Qualifying, which the FIA says was "unrelated" to the "human error".

"This issue in question meant Overtake Mode was not available after the red flag period during SQ1," read an FIA statement.

"When it became apparent that Overtake Mode was not active after the restart, it was then activated for a period of 27 seconds before being deactivated again.

"The FIA acknowledges that this unfortunate human error had an impact on the performance of certain cars based on the timing of their run and their position around the lap. The second and third periods of Sprint Qualifying were not affected."

The human error comes just five days after an "unprecedented" software glitch at the Bahrain Grand Prix in Malaysia caused several cars to grind to a crawl or a halt.

Sainz, who qualified last for Saturday's Singapore Sprint at 10am (build-up from 9am), live on Sky Sports F1 and Main Event, claimed half of the field had an advantage in SQ1.

"Half of the cars did their laps with half a second quicker engine than the others," said Sainz.

"There was another software issue with the cars this time around, and we were on the bad end of it.

"For whatever reason the FIA, like in Malaysia, at the end decide to do sporting equity and were happy to do half of the cars in qualy with higher power than the other half of the cars.

"A bit confused why the sport keeps doing different things depending on who is out in Q1 or who is out in lap one."

All of the main contenders progressed to SQ2 although Racing Bulls' Arvid Lindblad and Aston Martin's Lance Stroll would have fancied their chances of getting through.

Max Verstappen went on to take Sprint pole from Mercedes' George Russell and Ferrari's Charles Leclerc.

Sky Sports F1's Ted Kravitz:

"Unfortunate human error from the FIA, not the first time we've heard that.

"As far as Aston Martin are confirmed, their sporting director Andy Stephenson is still up with race control. They just want to understand what happened here today.

"They don't believe that anyone was doing their qualifying lap and then didn't have the extra half a megajoule available, what it's concerned about is the tyre preparation on the out-lap.

"Most of the drivers were on the radio saying they didn't have power, so they couldn't do the out-lap they wanted to do. That skews everything else, the rest of the computations they've done.

"While Aston Martin aren't making a protest, they do want to understand what's going on.

"They say the easiest thing would have been to stop the session and do it all again, but you've used your tyres by that time and that's not going to be possible."

Saturday October 10
9am: Singapore GP Sprint build-up*
10am: Singapore GP SPRINT*
1pm: Singapore Grand Prix Qualifying build-up
2pm: SINGAPORE GP QUALIFYING*
4pm: Ted's Qualifying Notebook

Sunday October 11
11.30am: Grand Prix Sunday: Singapore GP build-up
1pm: THE SINGAPORE GRAND PRIX
3pm: Chequered Flag: Singapore GP reaction
4pm: Ted's Notebook

*also on Sky Sports Main Event

Formula 1 is in Singapore for the last Sprint weekend of the season with Sunday's Grand Prix at 1pm (build-up from 11.30am) live on Sky Sports F1. Stream Sky Sports with NOW - no contract, cancel anytime