The former US Open champion triumphed on Saturday against an inconsistent Plíšková 0-6, 6-4, 6-1 in one hour and 55 minutes in Singapore.

A stunned Stephens lost the opening eight games before turning things around to win 12 of the next 15.

The hard-hitting Plíšková started red hot in what loomed as a one-sided contest before Stephens fought back with relentless hustle as the Czech went off the boil.

“I think obviously today was a great comeback,’ Stephens told reporters.

“I just made a couple extra plays on the ball. Tried something a little different. When I did that, it worked.”

Plíšková said she produced her “best set” of the year before the dramatic change.

“I don’t think I did that many things wrong in the second set,” she said. “Obviously, I lost a little bit (of) energy in the third set.”

It was an unexpected result after Plíšková’s early domination through power and precision to blitz through the first set in 31 minutes.

She pinpointed the lines to totally rattle a flustered Stephens, who uncharacteristically made a slew of errors.

After surviving an early break point, the one-way traffic continued in the second set with Plíšková breaking in the second game against a dejected Stephens.

The humiliation ended for Stephens when she broke Plíšková’s previously-impregnable serve in the third game and then started to find her range.

Plíšková’s first serve deserted her as a composed Stephens forced a decider and her momentum continued by capturing a break to open the third set.

Stephens rolled through against a slumping Plíšková to complete a monumental turnaround, as the former world number one fell in the semifinals for the second straight year.