The conversation about winning and losing tennis matches begins with the second serve.

Dominic Thiem outlasted Pablo Carreno Busta 6-3, 3-6, 6-4 at the Nitto ATP Finals Wednesday evening with this key battleground being the crucible of the final outcome.

The first serve always reigns supreme in our sport, delivering a healthy win percentage because of its power, freedom, and accuracy. But as soon as it’s missed, the gateway to breaking serve becomes illuminated. The first serve is essentially a red light to collecting return points. The second serve is as green as it gets.

At 4-4, 15/15 in the third set, as the match clock ticked over to two hours on the dot, Carreno Busta chased a first serve down the middle to Thiem’s backhand. It clipped the net and went long, and in so doing, the point flipped from red to green for Thiem.

Carreno Busta kicked in an 83 mph second serve, which Thiem thumped with a forehand return straight to Carreno Busta’s backhand. Thiem followed it up with a leaping run-around forehand winner back behind to the backhand. The match essentially ended right there.

It was the gateway point to victory, as Thiem would win seven of the next nine points to seal a very tight encounter. Both players had a winning record behind their first serves, and both players had a losing record behind their second serves. That’s more common in our sport than we realise.

The three main reasons second serves get beat up so much are because of the predicability of their location to the backhand return, the reduced speed at which they are hit, and the high volume that come back in the court, instantly putting the server on defence.

Carreno Busta’s fastest serve for the match was 122 mph, but his average second serve speed was 83 mph – just 68 per cent of his most powerful delivery. This dynamic allowed Thiem to mentally switch from defence to offence during the match as soon as the first serve was missed. The relationship between the speed of each serve, and the corresponding return speed, dictated who had first rights to enjoy offence.

Carreno Busta’s average first serve speed for the match was 109 mph, forcing Thiem to average 59 mph with his first serve returns – putting Thiem’s return speed at 54 per cent of the shot coming at him.

But how the weather changed when the first serve was missed.

Carreno Busta averaged 83 mph on his second serve, therefore enabling Thiem to average 80 mph with his second serve return – approximately a one-to-one ratio that let Thiem instantly wrestle control of the point.

Normally players step in closer to the baseline to return second serves, but not so with Thiem here in London. In this match, his average return hit point against a first serve was half a metre behind the baseline, but he then migrated back 1.7 metres behind the baseline to return second serves.

This was actually an improvement for Thiem from his opening-round loss to Grigor Dimitrov, where the Austrian averaged standing an astounding 3.3 metres behind the service line to hit second serves. That strategy works brilliantly on clay, but not so much on indoor hard.

Thiem essentially wants the ball to drop lower into his strike zone to crush it, rather than take the ball earlier and higher to get the ball back quicker to the server. Against Carreno Busta, Thiem’s average contact point against first serves was 1.31m, but that dropped to 1.19m against second serves.

The average net clearance of Thiem’s first serve returns was 1.16m, but that dropped to 1.06m against second serves as Thiem significantly upped his average return speed from 59 mph to 80 mph.

With Thiem serving at 5-4 in the third set, he made a first serve on the opening point and won it. Two second serve points followed, and he lost them both. He won the last three points of the match behind three first serves. Putting a first serve in the court at crunch time mattered a lot in this match, and then some.