An out-of-sorts Sharapova needed three hours and 12 minutes to wear down the typically obstinate Radwanska, the Russian moving to the top of the standings in the white group with two wins from two and just a final match against alternate Sam Stosur to come before the semi-finals.
"Today was an example of not playing my best tennis at all, fighting through it, hanging in there, and getting it done," Sharapova said.
It was perhaps a little surprising that it was Radwanska who made the better start to the match, her opening clash against an ailing Petra Kvitova on Tuesday doing little to establish form or momentum.
But the Pole, playing with her troublesome right shoulder heavily strapped once again, made a tenacious start to the match while Sharapova sprayed ground-strokes all around the stadium as she struggled to find her range.
A late finish to the scintillating Victoria Azarenka-Angelique Kerber match meant Sharapova and Radwanska did not even get on to court until nearly midnight Turkish time and the Russian seemed to struggle the most with that delay.
Sharapova was forced to come from behind in each of her opening two service games before finally finding some form deep into the first set, looking threatening on the return albeit never holding break points.
Radwanska stood firm, however, and snatched the first set, much to Sharapova’s consternation, when the Russian endured a poor game that saw her land just the one first serve in play.
An angry Sharapova looked set to get things quickly back on track when she broke in the first game of the second set, although it did take her five attempts before she successfully got ahead.
But two double faults in her very next service game saw Sharapova squander any momentum she had been building as Radwanska’s impressive defensive skills continued to see her get balls back in play that she had no right to even get a racquet to.
Things got even worse for the Russian when she missed a series of first serves and produced consecutive ground-stroke errors in the sixth game of the set to hand Radwanska a set and 4-2 lead in the match.
A clash between two such skilled and dogged fighters as Sharapova and Radwanska was never going to be a straightforward event, though, and this time it was the Russian’s turn to secure the immediate break back as she came around attacking on every ball.
The two players traded a third break of serve apiece for the set, Sharapova producing a fearsome game to go 5-4 before conceding her advantage once again as the serve continued to prove her undoing.
But, in almost an exact role reversal of the first set, the world number two stole the second set just when she looked to be floundering, a second serve ace ironically doing the damage before she went on to serve it out in the 12th game.
The final set was an understandably cagey affair; the vast majority of the Turkish crowd remaining transfixed in their seats as first 1am and then 2am came and went.
Sharapova was the first to get ahead as she broke, after a series of battling service holds from both players, in the fifth game; a forehand winner and a huge yell of “come on” heralding the game for the Russian.
But, as was the theme throughout the match, Radwanska immediately reduced the deficit, breaking back in the sixth game when Sharapova threw in yet another poor service game.
All of a sudden Radwanska looked the more likely victor as Sharapova’s serve again began to desert her, the Polish world number four holding with less trouble than her opponent.
But sheer determination and tenacity saw Sharapova through in the end as she broke for a second time in the set, in the 11th game as Radwanska’s normally indefatigable defence seemed to abandon her.
Sharapova, who is now almost certainly into the last four as the winner of the white group, then served out the match in the very next game.
Radwanska is still the favourite to go through to the last four as runner-up from the group and will face Sara Errani in her final round-robin stage match on Friday. Sharapova will take on Stosur also on Friday.