Recent literature has shown that an incumbent can use exclusive contracts to maintain supra-competitive prices, but only if he completely prevents a more efficient potential entrant from entering, and if the entrant is exogenously prevented from making exclusive offers. Such models cannot explain how exclusive contracts can lower welfare when they do not completely foreclose a small rival, when the rival can make exclusive offers, nor can they identify rudimentary relationships such as how a dominant supplier's size affects his incentive and ability to exclude and lower welfare. I formally model competition between a dominant input supplier and a small rival selling to competing downstream firms. I show that a dominant supplier can pay downstream firms for exclusivity, allowing it to maintain supra-competitive input prices, even when a small rival that is more efficient at serving some portion of the market can make exclusive offers. I also show exclusives need not completely exclude the small rival to cause competitive harm. The payment the dominant supplier makes for exclusivity must equal the incremental rents that the rival's input could generate if exactly one downstream firm sells goods using it.