Quick Commerce (Q-Commerce), defined as the ultra-fast delivery of goods within 10 to 30 minutes of order placement, has emerged as a disruptive force reshaping the global retail landscape. In India, platforms such as Blinkit, Zepto, and Swiggy Instamart have expanded rapidly in urban and semi-urban markets, fundamentally altering consumer expectations around speed, convenience, and accessibility. This study investigates the impact of Q-Commerce on traditional brick-and-mortar retailers and conventional e-commerce platforms, with special reference to Coimbatore District, Tamil Nadu. Adopting a descriptive research design and a mixed-method approach, primary data were collected from 150 consumers and 50 retailers using structured questionnaires and retailer interview schedules. Cluster sampling was employed to ensure geographical representation across urban, semi-urban, and rural segments. Statistical tools including Percentage Analysis, Weighted Average Mean, Chi-Square Test, ANOVA, and Pearson\'s Correlation Coefficient were applied for data analysis. The findings reveal that Q-Commerce has achieved deep consumer adoption driven primarily by delivery speed and convenience, causing significant declines in customer footfall, daily sales volumes, and profit margins among traditional kirana stores. A strong positive correlation (r = +0.864) was established between footfall decline and revenue erosion. While Q-Commerce and conventional e-commerce exhibit a largely complementary relationship through consumer behavioural segmentation, measurable competitive pressure on conventional platforms is intensifying. The study concludes with evidence-based recommendations for retailers, e-commerce operators, policymakers, and regulators to navigate the transformative and enduring impact of Q-Commerce on the Indian retail ecosystem.