While Barca were enjoying a perfect start to the La Liga season, Madrid picked up just one win from their opening four games and for a couple of 24-hour periods found themselves a massive 11 points behind Tito Vilanova's men.
That gap is still at eight points going into the seventh round of fixtures this weekend, but reigning champions Madrid at least appear to have put their early-season malaise behind them now.
Wednesday's 4-1 Champions League win over Ajax was Madrid's fourth successive win in all competitions, while last week they also thrashed Millonarios 8-0 in the Santiago Bernabeu Trophy.
Madrid coach Jose Mourinho, who questioned some of his players' commitment a few weeks ago, said: "Winning these consecutive matches is important for our aims and our confidence.
"The team was focussed (against Ajax), playing at their best with good individual movement and as a team. We played a very good match and we have to keep going.
"We cannot win every match but with this attitude, commitment, and approach to matches, individual quality becomes collective quality and it is normal that the results start to come and that the team improves."
While Madrid are just finding their form, Barca have started life under new coach Vilanova in magnificent fashion with nine wins from 10 games in total, with their only setback being a defeat to Madrid in the second leg of the Spanish Supercopa.
Barca midfielder Cesc Fabregas, who netted twice in last weekend's comeback win over Sevilla and then again in Tuesday's Champions League triumph over Benfica, sounded an ominous warning to Madrid by claiming: "We're playing better each time we play."
Vilanova, who has lost captain Carles Puyol and Gerard Pique to injuries, added of El Clasico: "I think we're coming into the match on form, at the moment we're playing at a good level, even though I would like to be able to call on all of my players for a match like this."
The game in Barcelona is not the only eye-catching encounter in La Liga this weekend, with second-placed Atletico Madrid hosting third-placed Malaga at the Vicente Calderon.
Along with Barca, those two clubs boast the only remaining unbeaten records in the division and Atletico are only two points off top spot after winning their last five games.
Local pride is at stake both in Valencia, where Los Che take on city rivals Levante, and in the north of Spain where struggling neighbours Athletic Bilbao and Osasuna clash at San Mames.
Osasuna are second-bottom with four points while Athletic, who last season reached the Europa League and Copa del Rey finals, are just one point and one place better off.
Elsewhere, Real Mallorca meet Granada on Sunday as well.
In the game on Friday, Sevilla fell to a 2-0 loss to Celta Vigo with goals from Iago Aspas and Enrique de Lucas enough to move Paco Herrera's side move into the top half of the table.
And on Saturday, Oscar Gonzalez's header 10 minutes from time secured a 1-1 draw for Real Valladolid and denied 10-man Espanyol their first win of the La Liga season.
The visitors were dealt a blow when Victor Alvarez was sent off just before half-time, but defied their numerical disadvantage to take the lead through Joan Verdu's penalty.
Valladolid were level 10 minutes later, though, when Oscar headed home Patrick Ebert's corner.
Getafe ground out a 1-0 win over nine-man Real Zaragoza thanks to Diego Castro's second-half penalty.
Ndri Romaric was shown a straight red card after just nine minutes, but it took until the hour mark for the visitors to go in front, when Alvaro Gonzalez became the second dismissal for tripping Pedro Leon and Castro scored from the penalty spot.
Getafe themselves were then reduced to 10 men for the final 10 minutes as Abdel Barrada also saw red but they held on.
Real Betis hit back from two successive league defeats by beating Real Sociedad 2-0.
Kick-off was delayed by 17 minutes at the Manuel Ruiz de Lopera Stadium because of a power failure.
Once proceedings got under way, Paulao headed the home side in front after 18 minutes and Ruben Castro made the game safe nine minutes from time.
Betis' night ended on a sour note with the dismissal of Mario for a second yellow card, but the points were already secure.
Rayo Vallecano registered their first win in five games with a 2-1 result over Deportivo La Coruna.
The hosts were 2-0 up within half an hour through Piti and Jose Carlos.
Depor were then given a lifeline just before half-time when Pizzi converted a penalty, but they could not find an equaliser.
Friday's La Liga Results
Saturday's La Liga Results
Sunday's La Liga Fixtures
Barcelona vs Real Madrid