It is the first time RU women's soccer has knocked off the #1 team in the nation but not the first time "any Rutgers team has beaten a #1 team..." I'm not sure about other sports but RU women's basketball has defeated AT LEAST 5 #1 teams that I can recall off the top of my head. I can't recall all of the years involved but RU has knocked off Tennessee, Penn State (1995?), ND (2000 or 2001), Duke (2007? in a regional final, in a season when Duke had defeated RU by 40 at the RAC in December), and most recently, UConn.
And RU almost made women's bball history after that win over UConn when it traveled to Knoxville, who rose to #1 in the next polls, for the famous "Clock-gate" game. RU led by one + had effectively defeated the Vols in a legitimate 40 minute game but the time-keeper stopped the clock for a couple of seconds, which was enough time for the refs to call a foul on RU AFTER 40 minutes had passed by. Tennessee made both shots and the win was awarded to them in the extended game. This was documented repeatedly on replays on TV, with the announcers incredulous that Tennessee got to shoot those foul shots. Had RU been permitted to win, it would have been the first time (and probably still the only time) that any women's bball team had defeated #1 in successive game, which is pretty difficult to do schedule-wise, when you stop and think about it.
Football was just one play away when it lost to Alabama at GS in 1980 and I believe that Florida was #1 in at least one poll when RU tied them in Gainesville to open the 1985 season. RU fumbled in the red zone in the last minute of play IIRC and didn't get to attempt a FG to seal with win.
I wouldn't be surprised if men's soccer has defeated one or more #1 teams during the glory years of the late 1980s and early 1990s but perhaps someone else could comment upon that.