Which incidents did not result in accidents because of the actions of the second pilot on board? In accordance with 14 CFR §25.1523 and §121.385c3, commercial airline aircraft must be operated by at least two pilots. This provision mainly bases on workload and pilot incapacitation considerations (see §25.1523-1).

I am looking for any incident reports of events, in which the second pilot (irrespecive of rank) on the flight deck has corrected a (fatal) mistake made by the other pilot or discovered a failure of some sort which was not discovered by the other pilot, and thus averted an accident. So not the daily flight in which everything is normal, but those in which something went wrong which was then corrected by the second pilot. 

Mostly, only events in which something goes wrong and which turn out as severe incidents or accidents are reported as such. These events are thoroughly investigated to learn from these events and make aviation safer. I am, on the other hand, interested in the other 99,99..% of events. Those events that are rarely reported, because everything turned out well in the end, "almost-accidents" that were prevented by the second pilot on board. 

Besides the obvious pilot incapacitation events, can anyone recall any specific events / flights and direct me to the respective (official or non-official) report, i.e. by the U.S. NTSB, the French BEA, the German LBA, the British &amp; Australian CAA, …?
During the 2005 Logan Airport runway incursion, the First Officer noticed the other plane and realized that they could collide. Telling the Captain to "keep it down", he pushed the control column forward and passed under the other aircraft as it took off. 

During United Airlines Flight 232, the actions of the flight instructor for the type, Dennis E. Fitch, brought in additional expertise that significantly contributed to success. E. Fitch joined the crew during the flight as an additional pilot.

On the day before Lion Air Flight 610 crash, that plane, already with problems, has been saved by off-duty pilot who correctly identified the problem (and suggested to disable the flight control system).