Emma Hayes felt it was an opportunity missed for Chelsea as their record-breaking 33-game unbeaten run being ended by a 2-1 loss to Brighton meant they failed to capitalise on a defeat for Manchester United.
United failed to beat Reading in the early kick-off, but the leaders and reigning Women's Super League champions Chelsea could not make the most of it, losing 2-1 to Hope Powell's team.
It was looking good for the Blues when Sam Kerr headed them in front from a corner in the fifth minute.
But Brighton levelled two minutes later through Aileen Whelan and stunned Chelsea with Megan Connolly's winner straight from a corner in the 77th minute.
Hayes left some big names on the bench and bemoaned a lack of intensity from her side, particularly in the first half.
"I thought the subs came in and offered what we needed. As a team, it wasn't good enough from us today on any level. Everybody in the dressing room knows that," she said.
With the league dominated by Chelsea, Manchester City and Arsenal in recent seasons and an impressive Manchester United side the surprise package of this campaign, Hayes said: "I think the United result and our result serves as a reminder that if you're not in it in this league you can be turned over.
"Our intensity and our aggression was really poor today. You have to take the game to the opponent and you have to work for spaces and chances and I don't think we did that well at all.
"We've given away two set-piece goals which I don't think we've done in my whole time here. They had three shots on target and scored two goals. That's extremely poor from us."
Chelsea have to pick themselves up for a midweek London derby against Arsenal and Hayes is determined to come back fighting.
"It was a bad result but it's not the end of the world," she said. "Everyone feels emotional after a defeat because we don't get them that often, but we have to stay calm. With losses comes learning and we have to bounce back quickly."
The Seagulls defended valiantly and could not hide their delight at the final whistle.
"It was a demanding, tough game," said coach Hope Powell. "We had to be disciplined with hard work and good effort and if you do those things you give yourself a chance of winning the game."
On the winning goal, she added: "I'll take some luck against a side like Chelsea - you take all the luck you can get."
In a long and impressive career in the game, former England boss Powell said the win over the champions was "up there".
"They're a top, top team. I'm sure it will sink in later," she said. "Chelsea's run had to end at some point and I'm just glad it was us. The most important thing was the three points."