Emma-Kate Lidbury finished fourth at the 70.3 Vineman event in California.
The former Oxford Mail reporter, who lived in Risinghurst, was in the leading group at the halfway point.
The 33-year-old finished the swim third in 25mins 43secs, before recording 2.24.10 for the bike leg.
However, this saw Lidbury, who is based in Santa Monica, drop further behind leader Meredith Kessler, of the United States.
A run of 1.27.01 saw her finish fourth, not enough to avoid an all-American podium.
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