Lewis, who graduated from the University of Arkansas, had the gallery's support during the tight round at Pinnacle Country Club.
She, Arimura and Recari each fired 6-under 65s in Round 2, while Ryu carded a 5-under 66 to join them atop the leaderboard at 10-under-par 132.
Knotted for fifth place one shot further back were world No. 1 Inbee Park (65), I.K. Kim (64), Pornanong Phatlum (65) and Ji Young Oh (66).
Mika Miyazato, who had led after the first round, tumbled to a 1-under 70, ending the day tied for ninth with Lydia Ko (66) at minus-7.