It was her 13th straight win this year, a run that has already netted titles at the ASB Classic in Auckland and at the Sydney International.
She hit 14 winners to Ivanovic's 35, but made a remarkably low four unforced errors compared to the Serb's 34.
After Radwanska cruised through the first set in just 27 minutes, Ivanovic, a former world No.1 and Australian Open finalist, tried to increase the tempo in the second, charging to the net more often.
But Radwanska's consistent placement and clever lobs wore down the crowd favourite, in what was the Pole's fifth-straight win over Ivanovic.
Earlier yesterday, fifth-seeded Angelique Kerber was beaten by the woman who ousted Serena Williams at the same stage last year.
Russian No 19-seeded Ekaterina Makarova won 7-5, 6-4.
"Seems like it was the same this year and last year. Unbelievable feeling," Makarova said.
"I really like to play here. The crowd is so perfect."
In the first men's match yesterday, fourth-seeded David Ferrer had a 6-2, 6-1, 6-4 win over No16 Kei Nishikori, of Japan, to reach the quarter-finals, where he will meet fellow Spaniard Nicolas Almagro.
Russian Maria Sharapova skipped into the quarter-finals with yet another effortless victory.
The No 2 seed beat Belgian Kirsten Flipkens 6-1, 6-0 in just 68 minutes.
Sharapova, who now faces Makarova, has dropped only five games in her four matches at Melbourne Park.
"I'm certainly happy to be playing this well, but it only gets tougher from here," Sharapova said.
Almagro earned a rocket ride into the quarter-finals when fourth-round rival Janko Tipsarevic retired hurt in their match.
Almagro was leading 6-2 5-1, with Tipsarevic struggling with what appeared a foot injury from late in the first set.
The Serbian called a medical time-out when down 5-2 in the first and returned with his ankle and foot heavily strapped.
The eighth seed was unable to finish the second set, calling it quits just past the one-hour mark.
Ferrer's magnificent chasing and defensive play was a feature of his two hour, 10-minute encounter against Nishikori.
"I played really good the first two sets - I didn't have any mistakes," said Ferrer.
Top results
4 David Ferrer (ESP) bt 16 Kei Nishikori (JPN) 6-2 6-1 6-4.
19 Ekaterina Makarova (RUS) bt 5 Angelique Kerber (GER) 7-5 6-4.
4 Agnieszka Radwanska (POL) bt 13 Ana Ivanovic (SER) 6-2, 6-4.
- AAP