NEWPORT BEACH, CA, USA -- The upsets continued at the inaugural Oracle Challenger Series event in Newport Beach, California, on Tuesday, as American Jamie Loeb breezed past her top-seeded countrywoman Christina McHale, 6-2, 6-4, in an 80-minute first-round encounter.

Loeb broke McHale four times in eight chances during their opening round of the WTA 125K Series event. Loeb also won 54 percent of her second service points, compared to only 30 percent for McHale. McHale was additionally undone by ten double faults.

Loeb raced to a 5-0 lead in the first set behind consistent, deep forehands and well-placed serves. McHale struggled with unforced errors throughout the whole set, and was unable to quell the tide for much of the opener.

However, Loeb blinked when serving for the bagel, watching a set point at 40-30 fall by the wayside, then hitting a backhand unforced error into the net to put McHale on the board. Two games later, though, Loeb fended off a break point, and McHale hit two unforced errors to cede the set to the unseeded American.

McHale then put herself into an early hole in the second set when she dropped serve in the first game, after hitting a backhand wide down break point. Surprisingly, this would be the only break of serve in the set, after an opening frame which featured four service breaks.

The No.1 seed cleaned up her game in the second set, hitting far fewer unforced errors, but McHale could never get to break point on Loeb's serve during the set. Loeb was hitting her spots perfectly, on her serve as well as her groundstrokes, and held for the match at 5-4 after McHale punched a final service return into the net.

Another first-round upset occurred when No.4 seed Francesca Schiavone was ousted by comebacking Slovak Anna Karolina Schmiedlova, 3-6, 6-2, 6-1. Schiavone, the former World No.4 and 2011 Roland Garros champion, was overcome by Schmiedlova in one hour and 48 minutes.

Schmiedlova, who was ranked in the Top 30 in 2015, is putting together a solid start to 2018. This result comes on the back of her successful qualification for the Australian Open, which was her first Grand Slam main draw appearance since the US Open in 2016.

One more opening-round upset was caused by Jil Teichmann of Switzerland, who defeated No.3 seed Taylor Townsend of the United States, 6-4, 6-2. The losses by McHale, Townsend, and Schiavone, coupled with No.2 seed Alison Riske and No.5 seed Sofia Kenin losing on Monday, means the tournament lost all of its Top 5 seeds in the first round.

A couple of Americans joined Loeb in the second round on Tuesday. No. 6 seed Sachia Vickery beat Russia's Evgeniya Rodina, 6-0, 6-3, making Vickery the highest-seeded player remaining in the draw. Also, Nicole Gibbs eliminated compatriot Julia Boserup, 6-4, 4-6, 6-0.

In additional first-round play, No.7-seeded Croatian Ajla Tomljanovic got past Yanina Wickmayer of Belgium, 6-3, 6-4, Sweden's Rebecca Peterson outlasted Bulgarian qualifier Elitsa Kostova, 4-6, 6-3, 7-5, and Carol Zhao of Canada overcame Chilean qualifier Daniela Seguel, 6-3, 2-6, 7-5.