Using the data from the Solar Dynamics Observatory, the Ahead of Solar Terrestrial Relations Observatory, the Global Oscillation Network Group (GONG), and the Large Angle and Spectrometric Coronagraphs, the nearly 90 degrees deflected eruption of a filament and the following coronal mass ejection (CME) occurring on the northern edge of AR 11123 on 2010 November 15 were presented in this paper. The filament was very small with the projected length of about 2.6 x 10(4) km and centered at about S23 degrees W 38 degrees. The potential-field source-surface model identified that the filament was located near the northern flank of a helmet streamer. The filament initially erupted northward to the nearby open fields with speeds from 151 to 336 km s(-1), resulting in a B7.6 subflare and some signatures of interchange reconnection. This suggested that the erupting filament interacted with the open fields at first. Then, guided by the highly-inclined open fields, it deflected about 90 degrees southward on the plane of the sky to the magnetic minimum in the streamer configuration. In addition, the CME with the width of 64 degrees and the central position angle of 221 degrees was also deflected obviously in the inner corona to attain its final direction. Because the eruption failed to penetrate the open fields, these results corroborate the idea that open magnetic flux can act as a magnetic wall while a streamer belt can act as a potential well for coronal eruptions in the Sun.