OHIO, United States (AFP) — The ever-positive Rafael Nadal remains a total tennis optimist as he begins his final preparation for the US Open, with the Spanish world number eight insisting that he is working constantly to turn this season into a success.

The 14-time Grand Slam winner is competing this week at the ATP and WTA Cincinnati Masters, which he won in 2013, the last time that he played.

After an injury absence which basically took him out of the last half of the 2014 season, the 29-year-old has been fighting all year to make improvements to a ranking which dropped to 10th after he failed to win a tenth Roland Garros title in June.

“The last part of the season is important. I want to finish feeling better than when I started,” said the eighth seed. “This is an important week for me.”

Nadal arrived in the Midwest after losing a Montreal quarter-final to Japan’s Kei Nishikori, who withdrew from the American tournament with a hip muscle problem that should be right for the US Open starting in a fortnight.

“I played OK in Montreal, but every week is a different test — a different story. I’m working more than ever to change the dynamic,” said Nadal.

With a two-hour rain interruption slowing a full day’s schedule, Ivo Karlovic still found time to produce the first upset of the week as the Croatian hammered 35 aces in a 6-4, 6-7 (1/7), 6-3 defeat of French 10th seed Gilles Simon.

Former top-10 American Mardy Fish began winding up his Cincinnati career with a defeat of Serb Viktor Troicki 6-2, 6-2.

Fish, who has suffered from a heart-scare problem and full-fledged anxiety attacks, will end his time on court at the US Open after dealing with his worries since 2012.

“I was a little surprised at my level. I hadn’t practised a ton or (practised) particularly well for a little while. I was struggling with my serve,” said the winner, 2010 finalist against six-time champion Roger Federer.

Fish moved into a second-round challenge with third seed and world number two Andy Murray, who comes to Cincinnati after his Montreal title at the weekend over Novak Djokovic.

“He’s pretty fantastic so far, he’s won a ton of matches,” Fish said of the Scot.

“He’s won more matches than anyone this year, so he’ll be tough.”

Australian Bernard Tomic reached the second round over Sergiy Stakhovsky 6-4, 6-3, while Joao Sousa of Portugal beat Germany’s Philipp Kohlschreiber 6-2, 6-7 (5/7), 6-2.

In the women’s draw, veteran Venus Williams and young compatriot Coco Vandeweghe both notched wins over Kazakh opposition.

The 35-year-old Williams came back after the rain interruption to finish off Zarina Diyas 7-6 (8/6), 6-4, while Vandeweghe beat Yulia Putintseva 6-3, 6-2.