In the evolving digital landscape, this study investigates digital technology complementary innovations (DTCI) in supply chains, comprising a buyer, new supplier, and existing supplier. It focuses on the roles of mature technology and leadership dynamics in collaboration. Key findings include: new suppliers exert maximum DTCI effort as followers, gaining more profit as leaders. Buyers' leadership role doesn't affect their DTCI efforts, but they prefer leading. With the existing supplier's low bargaining power, the buyer leans towards them for greater profits, reducing the new supplier's DTCI efforts. Success probability and digital complementarity positively affect buyer and new supplier's DTCI efforts but negatively impact the existing supplier.