* Nikkei eases 0.3 pct, edges towards psychologically key 8,500 * Renesas up on TSMC microchip business tie-up * Exporters remain under pressure as yen stays strong By Dominic Lau TOKYO, May 24 (Reuters) - Japan's Nikkei average dipped on Thursday, extending the previous session's sharp fall as investors remained skittish of a disorderly Greek exit from the euro zone, though U.S. stocks erased losses to end flat to higher, supporting sentiment. The Nikkei was down 0.3 percent at 8,532.05 by the midday break, and is down 0.9 percent for the week. If the benchmark were to end the week lower it would mark an eighth straight week of losses, its longest such run since 1992. "There was nothing massively negative coming out of the EU summit. The U.S. markets rebounded ... There is no real flow going through," a senior dealer at a European brokerage said. European Union leaders, advised by senior officials to prepare contingency plans in case Greece decided to quit the single currency, urged the country to stay the course on austerity and complete the reforms demanded under its bailout programme. After the morning session, data showed the HSBC Flash Purchasing Managers Index, the earliest indicator of industrial activity in China - Japan's largest export market - retreated to 48.7 in May, though not far from a final reading of 49.3 in April. Renesas Electronics Corp advanced 1.5 percent after the chipmaker said it plans to tie up with Taiwan Semiconductor Manufacturing Co in the microchip business.