Princeton fell to 5-1 with the loss and 1-1 in the Ivy League.
The league race saw a second upset when Cornell beat 14th-ranked Brown, 10-9. Sophomore midfielder Lauren Feinstein scored the game-winner for the Big Red with just 1:10 remaining.
Senior attacker Jen Bass led Cornell with five goals, and sophomore defender Liz Robertson added two scores in garnering Defensive Player of the Week honors.
Cornell--which had split two non-conference games against Bucknell and New Hampshire--finished the week with a 4-1 record and a 2-0 mark at the top of the Ivy standings.
Brown fell to 0-1 in Ivy play and 5-1 overall.
Yale completed a perfect week knocking off Massachusetts, 13-5, and beating Penn, 12-5.
The win over Penn opened the Bulldogs' Ivy season with a victory and raised their record to 5-0.
The Quakers, 12-1 losers to Temple earlier in the week, fell to 0-3 in the Ivy League and 1-5 on the season.
The Ivy slate is full this week as well, beginning with an important Harvard-Yale game today.
This weekend Princeton travels to Brown, Yale faces Cornell and Penn takes on Dartmouth.
Harvard also hosts third-ranked Loyola Sunday at Ohiri Field.