A second-round match between a 23-time Grand Slam champion and a 17-year-old wildcard may not seem like a top-billing clash. Serena Williams against a teenager is definitely not considered a top-billing clash either – she has lost just three times to teens at Majors and not once in the last six years.

But the manner in which Caty McNally tested the veteran and the manner in which the 37-year-old responded at the US Open on Tuesday made it the match of the rain-hit day.

The six-time champion battled from one set down to beat the world No 121 American 5-7, 6-3, 6-1 in one-hour and 54-minute in a performance that may have frustrated her during the match, but should please her after it.

After the manner in which she lost her last two finals in the span of month – Wimbledon to Simona Halep and mid-match retirement at Rogers Cup – this fighting win will give her a boost.

A few years ago, one would not imagine that Serena Williams needs a boost when she plays a Grand Slam. But in all honesty, she hasn’t quite the same ever since she returned to tennis after giving birth to her daughter. She has managed some good wins with three Slam finals, but stumbled against players who push her all over the court.

At the US Open, the six-time champion started with a 6-1, 6-1 thrashing of old rival Maria Sharapova and looked physically fit too. But if she sailed through the first round, the second-round challenge was enough to jolt last year’s finalist awake.

The last time an American teenager played a Williams sister at a Grand Slam, Coco Gauff became an instant star beating Venus Williams. This time, Gauff’s doubles partner Caty Mcnally made an impression with how she handled the big stage. The teen was not overwhelmed by the occasion or the opponent and said that she did not think about who was the other side of the net. She wasn’t even born when Serena Williams won her first US Open in 1997.

But with her effective, all-court game, tendency to serve and volley and slice and by mixing up her speeds, she troubled Serena Williams as few players have. But it was her composure after getting the crucial break at 5-5 that really made her stand out.

You can break Serena’s big serve, but consolidating it is a real challenge against the American. Serving for the set, she was down triple break point but clung on with a solid serve to take it 7-5. She saved three break points and converted the one she got. She would not get another look-in on Serena’s serve again, saving eight break points in total.

The set understandably frustrated Serena Williams. “Why are you missing?” she was heard saying. But if McNally was fearless in the first set, Serena became ruthless in the second and third.

She had only nine winners to 15 unforced errors in the first set but finished the match with 32 winners, including ten aces to 28 unforced errors. She crushed her winners, cleaned up her errors and roared her way to points. She came to the net more often and won 10 of her 15 approaches.

After getting her first break for the match, she prevailed in a two-deuce game to hold for 5-2. But serving to stay in the set, McNally saved 4 set points in a game that lasted almost 10 minutes, not allowing Serena Williams to end it on her serve.

The eighth seed did take the set and then turned into the version of her that can scare any opponent. In the third set, she lost only five points and none on her serve, winning 16 of the opening 17 points to seal a good win.

Asked to assess her game, she looked disoriented during the midnight interview saying: “Serena, you made way too many errors today. What were you thinking?”

But in the press conference after, she was a lot more positive and analytical about the match. “I think it’s great because I want to be able to win matches where I’m not playing my best, play players who are playing great, be able to come through. I need to be tested, I guess.”

With the test successfully negotiated, the path will only get harder for the player chasing a record-equalling 24th Grand Slam. In the third round, she will either face tricky Karolina Muchova or the giant-killing Su-Wei Hsieh. The slow start aside, this win should give Serena both confidence and a plan to avoid the same mistakes going forward.