Initial phase of COVID-19 infection is associated with the binding of viral spike protein S1 receptor binding domain (RBD) with the host cell surface receptor, ACE2. Peptide inhibitors typically interact with spike proteins in order to block its interaction with ACE2, and this knowledge would promote the use of such peptides as therapeutic scaffolds. The present study examined the competitive inhibitor activity of a broad spectrum antimicrobial peptide, Dermaseptin-S4 (S4) and its analogues. Three structural S4 analogues viz., S4 (K4), S4 (K20) and S4 (K4K20) were modelled by substituting charged lysine for non-polar residues in S4 and subsequently, docked with S1. Further, the comparative analysis of inter-residue contacts and non-covalent intermolecular interactions among S1–S4 (K4), S1–S4 (K4K20) and S1–ACE2 complexes were carried out to explore their mode of binding with S1. Interestingly, S1–S4 (K4) established more inter-molecular interactions compared to S4 (K4K20) and S1–ACE2. In order to substantiate this study, the normal mode analysis (NMA) was conducted to show how the structural stability of the flexible loop region in S1 is affected by atomic displacements in unbound S1 and docked complexes. Markedly, the strong interactions consistently maintained by S1–S4 (K4) complex revealed their conformational transition over the harmonic motion period. Moreover, S1–S4 (K4) peptide complex showed a higher energy deformation profile compared to S1–S4 (K4K20), where the higher energy deformation suggests the rigidity of the docked complex and thus it’s harder deformability, which is also substantiated by molecular dynamics simulation. In conclusion, S1–S4 (K4) complex has definitely exhibited a functionally significant dynamics compared to S1–ACE2 complex; this peptide inhibitor, S4 (K4) will need to be considered as the best therapeutic scaffold to block SARS-CoV-2 infection. © 2021, The Author(s), under exclusive licence to Springer Nature B.V. part of Springer Nature.