Driven by the dual forces of intensifying global technological competition and the “fast track” of technological iteration, R&D collaboration has become an inevitable strategic choice for enterprises to break through core technologies in key fields and seize the commanding heights of science and technology. Drawing upon combinatorial innovation theory, this study constructs an internal technological network at the micro-enterprise level using Chinese patent data to empirically examine the impact and underlying mechanisms of corporate R&D collaborative behavior on the acceleration of innovation in core technologies in key fields. The findings indicate that R&D collaboration systematically reshapes the topological structure of technological networks by expanding network scale, increasing network links, and strengthening edge weights, thereby significantly accelerating innovation in core technologies in key fields. This acceleration effect exhibits a distinct “technological selectivity”, with its benefits being particularly prominent for core technologies in key fields. Furthermore, the accelerating efficiency is jointly moderated by the regional technological ecosystem, network topological position, and the scale and dependency of cooperation. Consequently, it is imperative to construct cross-regional collaborative ecosystems, elevate the network centrality of enterprises, and adhere to a “moderation principle” to avert the negative shocks of collaboration overload. This study not only deepens the theoretical understanding of “how collaboration accelerates innovation” but also provides empirical support and policy guidance for optimizing the allocation of national strategic scientific and technological forces.