Top seed Serena Williams suffered a shock defeat to fellow American Madison Brengle in the second round of the WTA Auckland Classic on Wednesday to bring an abrupt end to her return to the court.

In her first tournament since losing in the semi-finals of the US Open four months ago, Williams was bundled out 6-4, 6-7 (7/3), 6-4 by the world number 72 in a two-hour, 13-minute arm wrestle.

Williams was looking for a bold showing in Auckland, both to prepare for the Australian Open and to celebrate her New Year engagement to Reddit co-founder Alexis Ohanian.

After blaming rust for her sluggish first-round win over Pauline Parmentier on Tuesday, Williams succumbed to repeated unforced errors against Brengle.

She started with an ace only to follow up with a double fault which exemplified the inconsistent nature of her game in the swirling wind.

Brengle dropped her second service game but at 4-1 down reeled off five consecutive games to take the first set.

There was a service break each in the second set in which Williams held and lost five set points before going on to take the tie-break 7-3.

The final set went with serve until Williams double faulted when serving to stay in the match at 4-5.