Cape Town - Proteas skipper AB de Villiers has taken responsibility for their batting collapse which cost them in the fourth ODI against Sri Lanka in Pallekele on Sunday.The Proteas were well set for a big total, with Hashim Amla's 71-ball 77 taking them to 110 for 1 after 20 overs, but they then succumbed to Sri Lanka's spinners and in the end managed only 238. JP Duminy, who partnered Amla during that partnership, made 97, but could not find sustained support from the middle order. Sri Lanka's three spinners bowled 29.4 overs in total and took seven wickets which slowed South Africa's progress significantly in the middle overs, leading to a string of quick dismissals. Tillakaratne Dilshan removed Amla leg before wicket and De Villiers (4) departed in Dilshan's next over. Duminy managed a 46-run stand with Faf du Plessis (23), but the Proteas lost six wickets for 33 runs."That period was the most disappointing thing," De Villiers told the ESPNcricinfo website. "Hash (Hashim) set us up really well to go big, but I think the previous wicket played a bit on our minds. The middle order created more turn than there was. "I think we were mentally a bit drained and we didn't support JP well enough. It was definitely, at the very least, a 260-score kind of wicket. Maybe 280, with our kind of batting line-up and the foundation we laid." De Villiers admitted he should not have lost his wicket at a crucial time."I've got to take a bit of responsibility because I got out to Dilshan and the guys coming (in) were a bit more aware of him, trying not to lose their wickets," De Villiers said. "I feel that Dilshan's not a bad bowler, but you can dominate him if you get on top of him, and I was trying to get that going. "Unfortunately, I got out playing my first attacking shot, and the rest of the guys following up were a bit circumspect about facing the spinners. Just as we'd get a partnership going, we'd lose another wicket." With their eight-wicket win Sri Lanka took an unassailable 3-1 series lead heading into Wednesday's final match in Colombo.Following the ODI series, a three-match T20 series awaits.