Danielle Carter struck two late goals to clinch a 3-0 Women's Super League win for Arsenal against Chelsea.
After a goalless first half England winger Rachel Yankey put the Gunners ahead before substitute Carter struck.
The result lifted second-placed Arsenal to within four points of Birmingham City with a game in hand.
A second successive defeat for Chelsea, who had previously gone unbeaten since the opening day of the season, has severely dented their title hopes.
In front of a crowd of 612, the Gunners, who were Chelsea's conquerors in that first game in the WSL's short history, completed the double over their London rivals.
But they did so only after coming unscathed through a hard-fought first half in which either side might have taken the lead.
Once Yankey had broken the deadlock with a 66th minute narrow-angled shot, however, Arsenal took control.
Eight minutes later Carter doubled the lead with her first WSL goal, a fine 20 yard effort that flew past goalkeeper Carly Telford.
And six minutes from time the 18-year-old England youth international bagged her second from similar distance to wrap up victory.