Observation of the baryonic B-decay (B)over-bar(0) -> Lambda(+)(c)(p)over-barK(-)pi(+)

We report the observation of the baryonic B-decay (B) over bar (0) -> Lambda(+)(c)(p) over barK(-)pi(+), excluding contributions from the decay (B) over bar (0) -> Lambda(+)(c)(Lambda) over barK(-). Using a data sample of 467 x 10(6) B (B) over bar pairs collected with the BABAR detector at the PEP-II storage ring at SLAC, the measured branching fraction is (4.33 +/- 0.82(stat) +/- 0.33(syst) +/- 1.13(Lambda c+)) x 10(-5). In addition we find evidence for the resonant decay (B) over bar (0) -> Sigma(c)(2455)(++)(p) over barK(-) and determine its branching fraction to be (1.11 +/- 0.30(stat) +/- 0.09(syst) +/- 0.29(Lambda c+)) x 10(-5). The errors are statistical, systematic, and due to the uncertainty in the Lambda(+)(c) branching fraction. For the resonant decay (B) over bar (0) -> Lambda(+)(c)(p) over bar(K) over bar*(0) we obtain an upper limit of 2.42 x 10(-5) at 90% confidence level.