Former Australian Open runner-up Collins powered through the opening set in 43 minutes and broke early in the second to take control of the contest on Court Two, as Olympic champion Bencic struggled to make her opportunities count.

Bencic, who has not gone past the Wimbledon fourth round, found her groove and threatened to break Collins back but could not prevent the 29-year-old American from extending her lead.

However, wayward serving by world No 52 Collins allowed Bencic to level at 3-3 and the 26-year-old Abu Dhabi and Adelaide champion stepped up her game to force a deciding set.

Bencic clenched her fists and let out a roar after holding serve in a fiercely-contested fifth game and kept calm under pressure later in the tiebreak to advance.