In the USA, any flight scheduled to be over 8 hours requires one extra pilot, and more than 12 hours requires a fourth pilot. Of course all this may change depending on how the new flight time/duty time rules play out this summer.
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.
Europe (EASA/EU OPS) has a max duty time of 13 hours (extendable in case of WX/Mechanical delays for another hour at Captains discretion). In case of 3 pilots (augmented flight crew) the max duty time increases to 18 hours, whereby 12 hours stick time may not be exceeded.