Rins was not headed from the moment he set the session's first benchmark time, producing several lap times good enough for pole.
In the end, he lapped the Texan circuit in 2m16.396s on his Monlau KTM, and ended up almost half a second clear of Qatar winner Luis Salom's similar Ajo-run bike.
Laglisse's Maverick Vinales closed the gap to Rins to 0.7 seconds with his final run, but could not improve on third place.
It was a best-ever Moto3 qualifying session for Jack Miller, the Australian ending up fourth fastest, though he was 1.9s behind the pacesetting Rins.
The battle to join Miller on the second row exploded as the flag fell, as several riders posted late improvements.
Niklas Ajo, Danny Webb, Isaac Vinales and Arthur Sissis all occupied the final row two places in the dying seconds but were bumped further down the top 10 by Jonas Folger and Alex Marquez.
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