The 21-time Grand Slam winner appeared to be in control of the match, taking a set and a break lead and serving for the match at 5-4 in the second set, but McHale saved a match point to break back and went on to ensure a decider was required. 

Nevertheless, Williams regained her composure in the third with her 12th ace sealing a 6-3, 5-7, 6-2 success. 

"She [McHale] definitely started to fight harder, and is clearly capable of playing great tennis," said the eight-time winner of the event.

"She showed it today."

Number three seed Agnieszka Radwańska of Poland was considerably more comfortable in securing a third-round berth in the tournament, an  ATP World Tour Masters 1000 event, as she overcame France’s Alizé Cornet 6-0, 6-1 in 68 minutes.

Romania’s Simona Halep fended off a second-set fight-back from Russia’s Daria Kasatkina to triumph 6-3, 7-5 and there was also an impressive 6-3, 6-0 win for Britain’s Heather Watson, who beat number 20 seed Sloane Stephens of the United States.

In the men's tournament, Uzbekistan’s Denis Istomin earned his first tour-level win of the year to set up a second-round clash against second seed and two-time former champion Andy Murray of Scotland.

Despite losing the first set against Croatia's Borna Ćorić, Istomin rallied to get the better of his opponent 4-6, 7-5, 7-5 in two hours and 46 minutes.

It ended a lengthy winless run for the Uzbek, whose last ATP World Tour win came against Britain's Aljaž Bedene at Moscow's Kremlin Cup last October.

Bedene will take on number 17 seed Roberto Bautista Agut of Spain in the second round after he defeated fellow countryman Roberto Carballes Baena, a wild card, 4-6, 6-2, 6-3.

Victory came just 24 hours after the International Tennis Federation ruled the Slovenia-born player was ineligible to represent his adopted nation in the Davis Cup. 

"I'm still shocked, to be honest," said Bedene, who is considering taking his case to the Court of Arbitration for Sport.  

Also booking their place in the second round was Italy's Andreas Seppi, who got the better of Donald Young for the second time this month, having also beaten the American at the BNP Paribas Open in Indian Wells.

Seppi won 80 per cent of his first-serve points to claim a 6-3, 6-1 win and now goes on to face number 27 seed Alexandr Dolgopolov of Ukraine.

America's Tim Smyczek saved nine of 13 break points on his way to defeating fellow countryman Tommy Paul, an 18-year-old qualifier, 6-4, 5-7, 7-5.

The opening round of the men's doubles saw Spanish duo Rafael Nadal and Fernando Verdasco beat Italy's Simone Bolelli and Seppi 6-3, 6-4 to ensure their progression. 

Action in Miami is due to continue tomorrow.