Brighton had been leading the Blues 2-1 when Lauren James equalised from close range in what looked a clear offside in Sunday's clash.
But the flag didn't go up and Chelsea went on to escape with a 2-2 draw and their season's unbeaten record in all competitions just about still intact.
Vidosic, the former Melbourne City boss who's been widely hailed for transforming Brighton's fortunes this season as they lie fifth behind only the WSL's big guns, admitted: "I'm almost a little bit disappointed.
"I think we had the opportunities to go 3-1 up and we didn't take them and then it felt like the result maybe scared us, that we were winning 2-1. We had it there."
Told that James's goal looked offside, he added: "It was hard to tell from the angle we have, but you hope not because then it cuts a bit deeper."
Chelsea had taken the lead in the 16th minute through Sandy Baltimore, but Marisa Olislagers levelled for the hosts six minutes later and Vicky Losada put them ahead before the break.
But though Chelsea went away with the draw, Vidosic had the satisfaction of being only the second manager to take a point off the champions in the league this season.
Though Manchester United narrowed the gap at the top to five points after they beat Leicester City 2-0, Chelsea's biggest worry was an injury to their world-record signing, US defender Naomi Girma, which forced her off before the hour mark in her first start.
Chelsea boss Sonia Bompastor was relieved to report "the injury doesn't look too bad".
A host of returning Matildas played bit parts after returning from their disappointing SheBelieves Cup campaign in the US.
Most were introduced as second-half substitutes after only returning to England late in the week, with Mary Fowler coming off the bench in the last 20 minutes to inject some life into Manchester City as they won 2-1 at Tottenham.
Vivianne Miedema scored in the 11th minute, while Aoba Fujino, who'd been part of the Japan team that crushed the Matildas in Houston, grabbed the second in the 78th.
Match of the day proved to be Arsenal's extraordinary 4-3 win over West Ham United at Borehamwood, featuring a fine second-half display from the Gunners' Australian midfielder Kyra Cooney-Cross after she'd been brought on in the 55th.
Three-one down after 51 minutes, Cooney-Cross helped orchestrate a remarkable comeback, with goals from Katie McCabe, Leah Williamson and a penalty from Mariona Caldentey in the space of six minutes, giving them the lead just after the hour mark.
