The tour's two month stay on European clay has traditionally been a productive time of year for Errani, and she started her Stuttgart challenge with a typically dogged performance to triumph, 7-6(8), 6-4.
Unlike many of her peers, Errani has already had plenty of competitive outings on the dirt in 2015, picking up a title in Rio de Janeiro and over the weekend running the mighty Serena Williams close whilst on Fed Cup duty.
Errani bounced back from this disappointment to win the decisive doubles alongside Flavia Pennetta and raised herself once more for a baseline battle of attrition against Radwanska.
"It was really tough. Sunday's Fed Cup matches were really tough and I was quite tired before the doubles but then Flavia and I played very well and it of course gave me a lot of confidence, which is important on clay," Errani said.
"But I think I played a really, really good match today. It was very long, long rallies and many good points. So, I'm very happy about how I performed after all those matches over the weekend."
For Radwanska, whose exit comes 24 hours after Caroline Garcia tripped up Ana Ivanovic at the same stage, it was a frustrating experience as she struggled to break through Errani's watertight defenses. The Pole led 5-3 in the first set and held a couple of set points in the subsequent tie-break, but a misjudged drop shot and an errant backhand let Errani off the hook.
"Obviously, a first round match against Errani is not fun," Radwanska said. "I think it was just a few points here and there that made the difference in the match. I had some chances and a few points that I just didn't finish."