Asian stocks opened lower after a selloff in US chipmakers deepened, overshadowing a plunge in oil prices on optimism over diplomatic progress toward ending the war in Iran.The MSCI Asia Pacific gauge dropped 0.4% with South Korea’s Kospi Index sliding almost 3%. In the US, a gauge of chipmakers extended a three-day rout to 12% and the Nasdaq 100 sank 10% from its peak, entering a technical correction.