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We evaluated the effects of a deficit-irrigation (DI) strategy in mature ’Lane late’ sweet orange (Citrus sinensis (L.) Osb.) trees grafted on two different drought-tolerant rootstocks, ’Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka) and ’Carrizo’ citrange (Citrus sinensis (L.) Osbeck x Poncirus trifoliata L.). Two treatments were applied: a control treatment, irrigated at 100% of crop evapotranspiration (ETc) during the entire season, and a DI treatment, irrigated at 100% ETc, except during phases I (initial fruit-growth period,) and phase III (final fruit-growth period, ripening, harvest), when no irrigation was applied. Flowering, fruit abscission and fruit growth of trees on ’Carrizo’ were more affected by DI than on ’Cleopatra’. Deficit irrigation reduced yield in both rootstocks due mainly to a decrease in the number of fruits. The phase most sensitive to drought stress was phase I. Moreover, DI altered fruit quality depending on the period when drought stress was applied. Fruit quality was modified by DI: total soluble sugars and titratable acidity increased when a severe drought stress occurred only in phase III but only increased the peel/pulp ratio if it occurred only in phase I. The quality of fruits from trees on ’Carrizo’ under DI was affected more than that of fruits from trees on ’Cleopatra’. Under DI in semi-arid regions ’Cleopatra’ mandarin can mitigate more the negative effects of drought stress on yield and fruit quality than ’Carrizo’ citrange.