Late Billy Vunipola try sees Saracens come from behind to win at Saracens
First-half Danny Care score and remarkable Joe Marchant try had seen Quins lead for much of second half
Leicester beat Northampton at Twickenham in Rob Horne send-off
Gloucester secure bonus-point win at Wasps
Sale leapfrog Newcastle at bottom with win over Falcons
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Harlequins 20-12 Saracens
James Law
BBC Sport at Twickenham Stoop
Laughs of disbelief in the press box after that Joe Marchant try.
It’s the worst kick of the night from Marcus Smith and yet it earns Quins a priceless seven points.
Owen Farrell then has an equally ropey penalty attempt for Sarries but gets no such luck...
Joe Marchant, con Marcus Smith
Image source, Getty ImagesGet this... you'll need to read it twice!
Marcus Smith lines-up the penalty kick at goal. It falters in the wind and doesn't have the direction, but, that doesn't matter one jot.
Instead, Joe Marchant shows incredible pace to chase the ball. The flyer beats every other player to it, plucks it out of the air and then grounds the ball. Unbelievable work.
Smith adds the conversion too.
Harlequins 13-12 Saracens
"I think it is a try."
The words of Luke Pearce to his TMO. Harlequins may have just scored the most extraordinary try...
Harlequins 13-12 Saracens
Tempers boil over, yet again, and with Saracens reacting badly to the decision the referee penalises them.
Marcus Smith puts the ball deep into the corner and Harlequins gain a second penalty from a shove at the line-out.
Harlequins 13-12 Saracens
James Law
BBC Sport at Twickenham Stoop
Sarries have come out all guns firing in this second half.
The hosts have largely contained them for now but it’ll need a Herculean display if they are to end the leaders’ perfect Premiership start.
Owen Farrell
The ever-accurate boot of Owen Farrell strikes again.
After so many phases inside the red zone, though, the visitors will be a tad upset that he wasn't taking a conversion.
Harlequins 13-9 Saracens
Image source, PARight then, look at these stats!
Harlequins have made 150 tackles so far and they have missed just seven. In contrast, Saracens have made just 26 tackles all game!
Here's one more for you, Billy Vunipola has made more carries than the entire Harlequins pack put together.
Harlequins 13-8 Saracens
Saracens are up to 18 phases but the roars of from the stands raise for Harlequins with every tackle. Chris Robshaw almost gains a massive, massive turnover but not quite.
Still Saracens press through their forwards until Owen Farrell, on the 25th phase, decides that he's had enough. He goes for the cross-field kick and that is charged down.
Harlequins 13-9 Saracens
Tim Visser knocked the kick-off on and Saracens march forward following the scrum through the powerful work of Billy Vunipola .
They build through nine phases with Vunipola again making key strides forwards. On the 14th phase they spin it wide and Alex Goode almost jinks his way through.
Harlequins 13-9 Saracens
Both sides are back out and we're ready for the second half.
There's good news from Harlequins at the break and that is that Paul Lasike, who left the field on a stretcher in the first half, is awake and comfortable. No further details right now but that's a positive update.
HT: Harlequins 13-9 Saracens
Hugh Godwin
BBC Radio London co-commentator
It's been a strange balance with Harlequins four points ahead and yet most of the play has been right to left with Saracens with the ball and attacking but that one breakaway try from Danny Care for Quins has edged them into the lead at the break.
HT: Harlequins 13-9 Saracens
James Law
BBC Sport at Twickenham Stoop
Image source, PAAfter a more attritional game this afternoon in torrid conditions at Twickenham, this match across the road is exhilarating.
Passion, quality, mistakes - what more could you possibly want?
This is what happens when the rain stops and both sets of players mean business.
FT: Northampton 15-23 Leicester
During Leicester's match against Northampton, England's Jonny May left the field with a shoulder injury.
Clearly, that was a concerning sight for both Tigers and England fans... here's the latest from the club on the matter.
Image source, Leicester TigersFT: Sale 20-7 Newcastle
Image source, Getty ImagesSale recorded only their second win of the season, and had to come from behind to do so, at the AJ Bell Stadium.
Steve Diamond's side outscored their opponents by three tries to one and the result means that Falcons have now won just one of their last eight Premiership Rugby encounters.
Read the full report, here.
FT: Wasps 21-35 Gloucester
Image source, Rex FeaturesBefore this afternoon, Gloucester had only won once on the road in Premiership Rugby since last November - 33-29 at London Irish in March.
However they put that record to bed today, and did so with aplomb, with a try-scoring bonus-point.
Take a look back at the match, here.
FT: Nothampton 15-23 Leicester
At the home of England Rugby, Leicester scored 17 unanswered first-half points on their way to beating Northampton.
The weather conditions weren't ideal for either side however the Tigers capitalised on their own chances and put in a very strong defensive shift to secure the result.
Despite the result not going in Saints' favour, the respect showed by fans and players alike for Rob Horne (the match was played in his honour) was tremendous to see. It was a great reminder of the unity shown in the game.
Leicester score 17 unanswered first-half points on their way to beating Northampton 23-15 in the East Midlands derby at Twickenham.
Read MorePremiership Saturday
With a little bit of time on our hands, let's take a look back at the results from earlier on and start over the road from The Stoop.
Image source, Rex FeaturesDanny Care has been the man of the moment in the first half as part of a fired up home side.
His intercept try, after 35 minutes, was the only five-pointer of the half but the lack of tries doesn't mean that this one is a boring one.
Both sides will look to sharpen up their discipline in kick-able positions in the second half and both will raise their intensities further. It's a corking arm-wrestle and just what you expect from a London derby.
Owen Farrell
Image source, Rex FeaturesNever in doubt from the visiting fly-half, it's time for both sides to take a breather.
Harlequins 13-6 Saracens
Hugh Godwin
BBC Radio London co-commentator
Danny Care is having an outstanding game, the 250 game milestone is one thing but he's actually producing it against the champion club of England tonight.
He is leading Harlequins brilliantly.