He wobbled a bit in the second, losing it by 1-6, but seems to have steadied the ship: *3-1 in the third, with Sandgren having had to battle to hang on to his second service game...
Phew! Thought he was going to blow that: 9-7 in the tie-break after squandering God know how many MPs, so he advances to the FQR courtesy of a 6-4 1-6 7-6(7 ) win.