On December 2, 2018, about 1940 universal coordinated time, a Cessna 172P, N98884, was substantially damaged when it was involved in an accident near Santa Rita, Guam. The commercial pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he conducted a standard preflight inspection and that the run-up and takeoff were normal. The pilot flew around the island and circled a nearby harbor at about 1,500 ft mean sea level before initiating a climb. The airplane was at about 2,500 ft when the pilot heard an obvious reduction in engine power. The rpm gauge decreased from about 2,500 rpm to 1,800 rpm before it abruptly lost power. There were no abnormal noises or visible leaks before the loss of power. The pilot initiated a forced landing onto an abandoned runway. The airplane landed long; it exited the end of the runway and impacted vegetation before coming to a rest. The airplane sustained substantial damage to the wings. Postaccident airframe and engine examination revealed no anomalies. The spark plugs were removed and exhibited wear consistent with normal operation. The propeller was rotated by hand, and drivetrain continuity was established to the accessory section. Thumb compression was established on all cylinders, and spark was observed on the spark plug leads. The fuel lines were examined and appeared normal; no blockages were noted.