After withstanding a fierce early challenge from the Italian, Kerber found another gear to prevail 7-5, 6-0 and end Vinci's bid to halt a major US Open subplot for a second time.
"I think I have right now more confidence going out there," Kerber said in her post-match press conference. "I'm not thinking about quarters, semis, or whatever. I'm just going there to playing a good match and to win.
"I know that I can beat everybody, and this is what gives me also a lot of confidence and motivation for going out there and playing with a lot of emotion."
Vinci and Kerber set the tone of the match early on; Vinci broke Kerber's serve in a marathon seven-minute opening game, before the German quickly grabbed the break back. In fact, Kerber trailed Vinci a break three times during the opening set, but each time she showed her mental toughness by never allowing Vinci to hold onto the lead.
The two played a game of cat and mouse throughout the first set, with both players showing off their variety and shot making; Vinci would reach a break point with a set of slices and drop shots, and Kerber would save it with a stinging inside-out forehand.
Kerber finally claimed the decisive break in the final game, winning the set and avoiding a tiebreak when Vinci was called for a foot fault on set point.
"I think the key of the match was the first set," Kerber reflected afterwards. "I mean, it was really close and tough. It's always difficult to play against Roberta.
"Keeping my mind a little bit relaxed, and staying in the moment - I think that was my key. Also for the first set to, be a little bit more relax and had not too negative, actually."
Already hobbled by a foot problem, losing the set by so narrow a margin seemed to suck the wind out of Vinci's sails. She didn't have much left in the tank against Kerber, who quickly broke three more times to run away with the match and return to the semifinals of the US Open for the first time since 2011.
Kerber struck 33 winners to 25 unforced errors during the match - just three of those errors in came in the second set - while Vinci hit 17 winners to 32 unforced errors. Vinci's serve was particularly vulnerable, serving at 40 percent first serves and winning just 57 percent of those points.
While the win moves Kerber one step closer to the WTA No.1 ranking, it spells out a different fate for Vinci. The Italian will fall out of the Top 10 come next week, having needed a run to the semifinals to keep up her ranking.
"Of course I'm so sad about today," Vinci said. "In general I played a great tournament. Now just will go home and take some days off; see what I have for my injury, and then we will see."
? WTA Insider (@WTA_insider) September 6, 2016