One-step self-etch adhesives are among the most popular adhesives to directly bond composite to tooth tissue, mainly because of their perceived ease-of-use. The aim of this randomized controlled trial was to evaluate the clinical performance of a HEMA-free 1-step self-etch adhesive (1SEa), as compared with a 3-step etch-and-rinse adhesive (3E&Ra). 267 non-carious cervical lesions in 52 patients were restored with a microhybrid composite Gradia Direct (GC), bonded in random order either with the HEMA-free 1SEa G-Bond (GB; GC) or the considered gold-standard 3E&Ra Optibond FL (OFL; Kerr). The restorations were evaluated after 6 months, 1, 2, 3, 5 and 9 years of clinical service for retention, marginal adaptation, marginal discoloration, caries occurrence and tooth sensitivity. Statistical analysis was done using a logistic regression model with generalized estimating equations (2-way GEE model). The patient recall rate at 9 years was 82.6%. The overall clinical success rate was 80.3% and 79.5% for GB and OFL, respectively. In total, 47 restorations (23 GB, 24 OFL) failed because of retention loss, severe marginal defects and/or discoloration and/or caries. A similar retention rate of 89.7% was recorded for both adhesives GB and OFL. Slight marginal defects and superficial marginal discoloration, though both still clinically acceptable, were significantly more observed at the incisal enamel side of GB (92.4% and 52.1%, respectively) than OFL (59.6%; 30.8%) restorations (p < 0.05). After 9 years of clinical service, class-V restorations bonded with the HEMA-free 1SEa performed clinically equally successful as those bonded with the 3E&Ra. However, more marginal deterioration, though still clinically acceptable, was recorded at the incisal enamel side for the 1SEa.