Lisa Evans netted twice, while Jordan Nobbs, Leah Williamson and substitute Emma Mitchell were also on target for Joe Montemurro's side. The result surpassed Liverpool's 9-0 win over Doncaster Belles in 2013.
Bristol City, which is now eight games without victory this season, pulled one back five minutes from the end when Yana Daniels scored on the rebound after her penalty was saved by goalkeeper Manuela Zinsberger.
The record win saw Arsenal leapfrog second-place Manchester City, which beat bottom club Liverpool 1-0, on goal difference. Gemma Bonner converted Caroline Weir's 20th-minute free kick to settle the contest in City's favor, leaving the visitors in last place on a single point.
Previous leader Chelsea dropped to third after its game at Everton was postponed due to a frozen pitch.
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