PARIS – In theory, the loss by Serena Williams and sister Venus in the third round of the Roland Garros women’s doubles Sunday might have had a silver lining.

But there also was a dark cloud.

Williams has had little match play in the last few months. So the necessity to go out and play every single day, between singles and doubles, was clearly having a cumulative effect.

Not that the sisters didn’t give it significant effort against No. 3 seeds Andreja Klepac of Slovenia and Maria José Martínez Sánchez of Spain.

But it wasn’t enough.

They could have lost in straight sets – probably should have, as Klepac and Martínez Sánchez served for the match at 5-4 in the second set.

But they fought to win the second-set tiebreak before fading in the third set and lost, 6-4, 6-7 (4), 6-0.

Slow-motion serving by Serena

The concern after this match went well beyond the defeat in doubles.

Because by that third set, Williams was just lobbing her serve in.

She admitted she hasn’t gotten the velocity back on her powerful delivery yet, since having daughter Olympia and having to work hard to get her core muscles back on point.

But 117 km/hour? That’s less than 73 mph. Almost in reverse slow motion, by Williams serving standards.

Below are some of the speeds of Williams’s serve in that one game she served in the third set. Most of those were first serves.

It wasn’t just on the serve.

At one point, down in the match, Williams had an opportunity to put away an easy overhead with a roar – and perhaps dent something in the process. In her previous matches, she had done just that.

But this time, Williams opted to hit a slow-motion overhead that wouldn’t have cracked an egg on contact.

Playing Sharapova Monday

If there’s an issue with the shoulder, arm or something in between, it could cast a completely different light on Williams’s fourth-round clash with Maria Sharapova in singles Monday.

The two haven’t met in 2 1/2 years, since the quarterfinals of the 2016 Australian Open. But it’s a highly anticipated matchup even if the head-to-head is heavily lopsided in Williams’ favor – 19-2, to be exact.

Sharapova’s two victories both came back in … 2004.

Williams has no interest in anything but continuing that dominance.

But if she can’t serve any harder than that, she’ll have a lot of trouble.

Was she saving her arm for the singles? Will it feel better when she comes out on Monday? And – worst-case scenario – if Williams feels she can’t serve full out, she’d certainly consider pulling out.

No chance she wants to lose to Sharapova, if she’s not fit to compete.

So much to contemplate ahead of this encounter.

Old grudges

The doubles match was a particularly delicious matchup in the sense that there was most definitely no love lost between Serena and Martínez Sánchez.

Here’s what it looked like:

The enmity dates back nearly a decade.

In 2009, at this very tournament, the two faced off in a fourth-round singles match that was won, 6-4 in the third, by Williams.

But early in the match, Williams hit a shot she was certain grazed Martínez Sánchez’s arm. The Spaniard wouldn’t cop to it, saying it had hit her racket. There wasn’t anything chair umpire Emmanuel Joseph, who hadn’t seen it, could do if Martínez Sánchez didn’t admit to it and concede the point.

“I looked at her dead in the eye, I said: ‘Why? Just be honest if the ball hit you or not,’ ” Williams said. “I mean, hello, it totally hit her. She was just, like, she wouldn’t even look at me. She looked down, and I just have no respect for anybody who can’t play a professional game and just be really professional out here,” she said.

“So the ball hit her body, and therefore, she should have lost the point instead of cheating,” Williams added. “I would never do that. I’ve never done that. I’ve never sunk low, and I would never do that to anyone on this tour and I never have.”

The microphones on court picked up some strong words. “I’m going to get you in the locker room for that; you don’t know me,” she said. And then, to Joseph, she added, “She better not come to the net again.”

The two met again a few months later, at the US Open. And they met twice more in singles, the last time in 2012. Williams won all of those.

Williams is savvier these days about the on-court microphones, you’d think. But it was clear that she had not forgotten the incident, all these years later.

She reminded chair umpire Kelly Thomson Sunday to make sure she enforced the rule. And the way these two teams were going at each other at the net, it well could have happened again.

Interestingly, they had met just once before in doubles. That came at the end of that 2009 season.

Williams and Williams qualified for the year-end Tour finals in doubles, and faced Martínez and Nuria Llagostera Vives in their first match.

They lost that one as well, 2-6, 6-4, 10-8 in the match tiebreak.

History will note that the sisters were a right mess in that one.