Weed infestation induces intense competition with the sunflower crop for soil nutrients, space, and light, causing significant yield losses of the sunflower. Therefore, a study was undertaken during the years 2013–15 at the College of Agriculture, University of Sargodha, Pakistan, to determine the effect of Cyperus rotundus infestation on various morphological and biochemical traits. Initially, a screening experiment was carried out to screen against C. rotundus infestation. Later on, crosses of selected cytoplasmic male sterile and restorer lines were attempted to develop F1 progenies, which were compared with commercial hybrids along with parents. There were 6 parental lines (3 A and 3 R lines) along with 9 single cross combinations obtained from these parents. The experiment was carried out in complete randomized design having factorial arrangement and three replications. Weeds in one of the regimes' latter called as control were completely absent, while in the weed infestation regimes 5 and 10 plants of C. rotundus were maintained. Results showed that C. rotundus infestation causes significant damage to the sunflower plants. Generally, cross combinations showed a decrease of leaf area by 440% and 264% 61% and 49% for chlorophyll contents, 133% and 191% for head weight under low and high weed infestation regimes, respectively. However, antioxidant activity increased by 44% and 49% under low and high infestation regimes induced by C. rotundus. Sunflower genotypes also showed variability in competitive ability against C. rotundus weed. Cross combinations coded as (A10 A7 and A2) showed a lower comparative decrease for seed yield and oil contents when compared with standard hybrids in the presence of C. rotundus. The development of sunflower hybrids with better competitive ability in the presence of weeds such as C. rotundus may be able to enhance plant development and lower yield losses in sunflower fields with minimal use of herbicides.