Slow slip and slow earthquakes (SSEs), driven by transient aseismic deformation along the subduction interface, are proposed to affect the initiation of megathrust earthquakes. Prominent examples, as inferred from geodetic and seismic observations, include the 2011 M9.1Tohoku-Oki,, the 2014 Mw8.1 Iquique (Chile), and the 2014 Mw7.3 Guerrero (Mexico) earthquakes. Understanding the conditions, such as 3D geometry, governing the dynamics of SSEs and, specifically, its interaction with megathrust earthquake initiation has the potential to fundamentally advance our understanding of subduction zone faulting. However, since observational coverage of subduction zones is limited and direct monitoring of earthquake nucleation phases is currently impossible, the physics underlying deep stress buildup remain elusive. We here present the numerical simulations of long-term quasi-dynamic slow slip cycles in the so-called Guerrero seismic gap to explore the physics of several Mw>7.0 transient slow slip events and their significant role in the long-term plate coupling (Perez-Silva et al.,2021). Our model suggests that the flat-slab segment of the Cocos plate aids the SSE large magnitudes and long recurrence intervals and also leads to significant shear traction concentration at the base of the seismogenic zone. We then use these transient shear traction as the initial condition for a 3D dynamic rupture scenario of the 2014 Mw7.3 Guerrero earthquake. We show that stress concentrations caused by the deep SSEs are significant enough to affect the initiation of spontaneous earthquake dynamic rupture.