A method of increasing output of a combined cycle power plant with supplemental duct firing from a heat recovery steam generator (HRSG) during select periods includes guiding a reheat steam flow to at least one reheat attemperator fluidly connected to the HRSG during the select period. The method further includes increasing reheat attemperation water flow through the at least one reheat attemperator, decreasing a set point temperature of the at least one reheat attemperator for the select period to a lower set point temperature, and raising power output of the combined cycle power plant during the select period.