Jan 21 (Reuters) - Australian shares are expected to fall at open on Friday, pressured by a likely drop in the shares of mining giant Rio Tinto (RIO.AX) as Serbia revokes the company"s lithium exploration licences, while weak cues from Wall Street will further sour sentiment. The local share price index futures were down over 0.91%, a 163.4-point discount to the underlying S&P/ASX 200 index (.AXJO) close. New Zealand"s benchmark S&P/NZX 50 index (.NZ50) snapped a two-day fall to open 0.15% higher at 12,515.82.