Davis had Kvitova under pressure throughout the match, breaking early and leaving the Czech to play catch-up.
"I was down each set, I really had to fight a lot," Kvitova said in her post-match press conference. "I had to come back in both sets. She was playing really well."
Kvitova managed to break back with the American serving for the first set at 5-4, then ripped through the next two games to steal away the set. But she was back in the same position late in the second, and responded the same way. She dictated play with her tricky lefty forehand, breaking twice to fight through after an hour and fifty minutes.
Kvitova's late-season resurgence - which saw her claim the title at the Dongfeng Motor Wuhan Open earlier in the Asian Swing - solidifies her spot at the top of the table at the Huajin Securities WTA Elite Trophy Zhuhai.
Niculescu overcame a slow start against Bertens, struggling to hold serve against the Dutch player. But she found her foothold to break twice and rattle off five straight games to take the opening set.
It was smooth sailing in the second set, with Niculescu breaking twice to build up a 5-2 lead. Bertens found a second wind to get one of the breaks back, but Niculescu had pulled too far ahead and rolled to her straight-sets victory after just under an hour and a half.
"I started a bit slow, but I played Kiki last year so I knew a little bit her game," Niculescu explained in her post-match press conference. "But when I played her she was ranked No.130, and this year she did that semifinal in Roland Garros, she's improved a lot."
It's Niculescu's second final of the season as well - after suffering early losses throughout the year, she reached the final at the Korea Open, where she lost to Lara Arruabarrena 0-6, 6-2, 0-6.
But no matter how her season is going, Luxembourg seems to bring out the best tennis from the Romanian - it's her third final here, after runner-up appearances in 2011 and 2012.
"I really like it here, I think that when I come here I just feel good mentally and physically," Niculescu explained. "I think it's just step by step. This tournament was very packed and there were so many good players here. It was a tough competition and I'm glad to be here in the final again. It seems I love this tournament!"