Serena Williams continued to make history last night as she defeated Elina Svitolina 6-3 6-1 to reach the US Open final.

In defeating the Ukranian world number five, Williams made her 33rd Grand Slam final, making her second on the all time list and just one behind Chris Evert for finals made.

She dominated Svitolina from start to finish and will face Candian Bianca Andreescu for another chance to win a record-equalling 24th major title.

She has had this chance numerous times in the last three years but Williams has not been able to convert. It can be down to the opponent or extenuating circumstances, but also some of the American’s strengths letting her down.

The serve seems to be letting her down

In her first 25 major finals, Williams won a staggering 21 times, and between Wimbledon 2012 and Wimbledon 2015, she won eight straight finals in Grand Slams.

However, since winning her 21st Grand Slam, the American has been in seven major finals and suffered five losses. Surprisingly, it has been her serve that has been the biggest letdown.

Throughout her storied career, Williams’ serve has dug her out of many a hole and according to many experts is regarded as the single greatest shot in women’s tennis history.

As can be seen in the chart below, in all five of the final losses since 2016, Williams’ win percentage on her serve was not higher than 56%.

She won 36 of 48 points on her serve last night, making that a 75% win rate. She will need to do that on Saturday night as well to win and reverse the trend of the last three Grand Slam finals in particular.

Longer points are her kryptonite

It should come as no surprise that as an athlete gets older, the physical demands of the sport they play seem harder.

In tennis, baseline play becomes harder with age and in the biggest of matches, it can be a key barometer.

As Williams has experienced since 2016, when Grand Slams suddenly became harder to win for her, opponents are looking to keep the ball in play more and asking Williams to take risks. This is proving to be catastrophic as a rally goes beyond 10 strokes, as the chart below shows.

Even Williams’ one-two punch that she is so well known for has seen a decline in major final losses, so it may be a lack of confidence and matches throughout the season that may be hindering her.

Last night, it did not matter as much because of her domination from the first point, but Williams will have to be wary of allowing a younger Andreescu to move her around and extend the rallies in the final.

Age and circumstances leading to more off days

We all know what happened in last year’s US Open final against Naomi Osaka and that unquestionably played a part in the thrashing for Williams.

But a straight sets final loss is something she has experienced in four of her last six Grand Slam finals.

In some finals, her opponents played lights out tennis to win and nothing the American did made any difference. But sometimes, her game inexplicably crumbled on the biggest stage.

Paul Annacone, former coach of male greats Pete Sampras and Roger Federer, said as you get older, you are going to have more bad days. Also, winning does not feel as good, but losses hurt more.

Whether Williams wins or loses on Saturday, because of her stature and ability, she is likely to be in more finals next year. But she may never get a better chance to equal the all time record, because she is not getting any younger.