Serena Williams is on a streak that doesn't appear to be in jeopardy of ending any time this year.

WTATennis.com reported that Williams throttled Madison Brengle 6-0, 6-1 in the first round of the Mutua Madrilena Madrid Open to run her 2015 winning streak to 21 matches and her total winning streak to 24, dating back to 2014.

Serena Williams' biggest challenger at the French Open is Angelique Kerber?

Williams needed just 55 minutes to conquer Brendle, who was coming off the best tournament finish of her career - a semifinals appearance at the Porsche Grand Prix in Stuttgart, Germany last week.

While Williams made quick work of the upstart Brendle, all of her potential challengers for the French Open title later this month at Roland Garros continue to play inconsistent tennis.

World No. 2 Simona Halep lost her opening match in Madrid to Alize Cornet, who defeated Williams twice in 2014 - long before Serena re-established her dominance.

It was Halep who last defeated Williams in a WTA Finals round-robin match in October. The 6-0, 6-2 loss was one of the worst in Williams' career.

No. 12 Angelique Kerber, who capped a surprising run to the Porsche Grand Prix title last week by ousting No. 5 Caroline Wozniacki in the final, also fell in the first round in Madrid, losing a three-set match to Sam Stosur.

Wozniacki had just defeated Halep in the semifinals and may be the most ready to challenge Serena. She did win her first-round match in Madrid.

As did world's No. 3 Maria Sharapova, who defeated Timea Bacsinszky 6-2, 6-3 after getting bounced in the second round at Stuttgart. Meanwhile, No. 6 Eugenie Bouchard lost her sixth straight match, a 0-6, 6-3, 6-3 affair to Barbora Strycova.

And for good measure, Serena's sister, Venus, also was bounced from the first round by Victoria Azarenka 6-3, 7-5 in Madrid.

Serena has to figure to be the heavy favorite, not only at Madrid, but at Roland Garros as well. If she can add the French Open to her Australian Open title, she will enter the second half of the Grand Slam season with a realistic chance of winning the Grand Slam and perhaps even going undefeated in 2015.

Do you think Serena Williams will lose a match in 2015? Comment below or tell us @SportsWN.