The points gap for coach Gerardo Martino's side was helped by Lanus' first defeat, 3-1 away to San Martin in San Juan.
Lanus' defeat enabled River Plate, who wore a new black strip to celebrate the 75th anniversary of their Monumental 1978 World Cup stadium, to climb above them into second place after they beat Atletico Rafaela 3-0.
With four matches to go in the Clausura championship, Newell's have 32 points, River 29 and Lanus 28.
Newell's, at their Marcelo Bielsa ground in Rosario, met Boca in the second of three clashes in a week between the two sides.
Both fielded a number of reserves, resting key players for Wednesday's second leg of their Libertadores Cup quarter-final at the same venue.
Thursday's first leg at Boca's La Bombonera was a 0-0 draw.
Peru midfielder Rinaldo Cruzado gave Newell's an early lead with a penalty after he had been fouled by goalkeeper Sebastian D'Angelo.
The only possible joy Boca could have taken from the match was that the result did not benefit their arch rivals River, now Newell's closest challengers for the title.
River, in their best performance of the championship, wrapped up their win in the opening half hour, starting in the eighth minute with left-back Leonel Vangioni's searing drive from 25 metres that goalkeeper Guillermo Sara got a hand to but could not stop.
"It's a special day for all the fans, [the win] is a prize for them," River coach Ramon Diaz told reporters.
"It was one of our best first halves... we needed a show of what the team is capable of," he added.
"Everything is so even in Argentine football that the top team can lose to the bottom. We knew [San Martin] were strong at home," Lanus coach Guillermo Barros Schelotto.
