General Brazilian
perder o ritmo no final / desacelerar no final
Most commonly used in both formal and informal contexts
Rio de Janeiro
perder a força / afrouxar no final
Common colloquial usage
São Paulo
perder o gás / desacelerar
Business and sports contexts frequently use 'perder o gás'
Portugal
perder força no final / desanimar no final
Portuguese speakers may also use 'arrefecer'