The case is Cousin v. Bennett. During jury selection, both sides struck various jurors, all of them white. When another panel of potential jurors came up, the prosecution struck the first juror on the list, who is black. Summarizing its holding, the Court of Appeals said, "Petitioner argues that the fact of the prosecutor’s challenge to the only African-American prospective juror to be called for voir dire was sufficient to establish a prima facie showing that the challenge was racially motivated. We disagree."
While in certain circumstances removing the only black potential juror may violate Batson, this is no such case. Here's the Second Circuit's reasoning:
Among other factors, the manner in which a prosecutor exercises peremptory strikes may be relevant to whether a prima facie showing was made. For example, if a prosecutor who possessed no information about prospective jurors other than what was visible from their appearance, proceeded to challenge the only African-American juror in a venire of sixty, or if a prosecutor’s remarks or questions in the course of exercising a single challenge indicated racial motivation, the single challenge might well be sufficient to sustain a prima facie showing of a Batson violation.
The circumstances of this case, however, were quite different. As explained above, by the time the prosecutor challenged Smith, he had already challenged fourteen (non-African-American) prospective jurors. The prosecutor, furthermore, did not select Smith for challenge out of a larger number of jurors. At the time the prosecutor challenged her, she was the only juror eligible to be challenged. Finally, the prosecutor had received information about each of the jurors, including Smith, from their questionnaires and then answers during voir dire, which information could have informed his decision.