A brave display from Alex Bolt was not enough to keep the Australian in the ATP Tour's Hall of Fame Open as he went down in three sets to American Jack Sock.
It was looking promising for Bolt, who made it to the main draw when he beat American Ryan Harrison 6-0 6-7 (7-2) 7-5 in qualifying, took the first set 6-3 but then succumbed 6-4 6-3.
Bolt's defeat leaves Jordan Thompson as the lone Australian in the draw.
The No.7 seed will meet Japan's Yuichi Sugita for a place in the quarter-finals on Wednesday.
Among those joining Thompson in the last 16 on Tuesday were Tennys Sandgren, Ivo Karlovic and Steve Johnson.
Sandgren beat Joao Sousa 6-4 6-7 (7-3) while wildcard Karlovic defeated Bernabe Zapoara Miralles 6-7 (7-5) 6-1 6-4.
American No.6 seed Johnson beat compatriot Denis Kudla 7-6 (7-3) 3-6 6-4 to advance.