(Reuters) - Angelique Kerber moved a step closer to turning a dream goal into reality with a hard-fought win over Barbora Strycova to reach the quarter-finals of the Western & Southern Open in a hot and humid Cincinnati on Thursday.

The Australian Open champion's 7-6(5) 6-4 victory over the Czech put the German world number two just three wins away from leapfrogging Serena Williams, absent from this event, at the top of the WTA rankings for a first time.

"It's the goal one day to be number one, but if it happens and when it happens, whatever," the 28-year-old told ESPN, adding that everyone was reminding her how close she was to topping the rankings as she tried to block out the thought.

"I would not be putting this pressure on myself here. I'm just trying to play my best tennis."

Kerber, enjoying her best season, including a Wimbledon final appearance and silver medal in the women's singles at the Rio Olympics, claims here improved serve and on-court attitude have been key to her rise.

"Mentally, I'm more quiet," she said. "I think I can put the emotion right now in the right place and that helps me to play really good.

"I've had a lot of ups and downs in my career, but I'm having the best year of my career and it's still not over," the left-hander said. "It's amazing what's happened in the last few months... it's just incredible!"

Kerber was her usual tireless self against Strycova, scurrying to extend rallies and wearing down her rival.

In the opening set tie-break, she drew errors from her Czech opponent and then closed it out with a precise backhand pass.

Strycova continued to hold her own in the second set but Kerber won the key points, breaking in the ninth game before confidently serving out.

Next up for Kerber is Spain's Carla Suárez Navarro, who beat Roberta Vinci of Italy 6-1 7-5.

Third-seeded Simona Halep notched her 12th win in a row with a 6-1 6-2 thrashing of Australian qualifier Daria Gavrilova, beating the heat by finishing in 53 minutes.

"Yes, it's very hot here," the Romanian said. "After the first set the sun hit me very strong so I didn't have too much energy. I'm really happy that I could finish."

(Reporting by Larry Fine in New York; Editing by John O'Brien)