The American, who was offered a wildcard entry to Cincinnati, was unable to battle past Pliskova, who prevailed in a 7-5 6-1 victory.
WTA Draw confirmed for 2022 Western & Southern Open including Serena Williams - Emma Raducanu
After the match, Williams revealed she had committed too many errors, while her opponent raised her own level in the second set, which ultimately determined the match.
"She raised her game in the second set and I just made too many errors," admitted the seven-time Grand Slam champion. "But definitely not an easy first round.
"And she's been playing well, I guess, all year? I really don't know. But she played well today against me."
Williams, 42, has played three matches this summer and she has lost all three. Earlier this month in Washington, Williams played her first singles match in a year. The WTA legend is scheduled to compete at the US Open later this month, but has made no mention of when she will eventually hang up her racket.