Li Na kept alive her hopes of reaching the semi-finals of the WTA Championships with a resilient and polished performance in a straight sets win over Angelique Kerber on Thursday.
The former French Open champion from China's 6-4, 6-3 win over the hard-working German may have also had something to do with the energy Kerber expended while earning match points in a massive three-hour effort against world number one Victoria Azarenka the night before.
Kerber nevertheless started well, breaking serve almost at once and holding her lead until 4-2.
But once Li had broken back for 4-4 she was more nimble of step, more flat-hitting of ground stroke, and eventually more motivated for success too.
By the end of the first set Kerber was becoming wayward with her serve and looking discouraged, which prompted some very intense in-your-face exhortations from coach Torben Beltz.
Li by contrast was nodding relaxedly at comments from her new coach Carlos Rodriguez, of whom she says: "He makes me a little bit stronger in the mind as well as in tennis."
Such qualities came in useful when Li was confronted with her early deficit, as did her liking for bold stroke-making.
She was particularly potent with sharp cross-court backhand angles in making the break back and when she maintained similar pressure in her next return game Kerber cracked.
The woman from Wuhan engineered two set points for herself, often threatening the Kerber second serve, and on the third Kerber delivered a costly double fault, her sixth.
It changed the match. Li broke again at once in the second set, and although Kerber bravely chiselled out a break back Li broke twice more, penetrating increasingly with her raking drives.
Kerber's resistance never completely disappeared and included one innovative double-handed shovel shot that launched a remarkable lob over her head while facing the wrong way.
But it made little difference, and if the eight-seeded Li can do well against Azarenka on Friday, she could yet qualify against the odds.