Having provided the free-kick for Lewandowski to head home the first, defensive midfielder Sahin then slammed home a goal of his own on 44 minutes before Lewandowski added his second in the first minute of stoppage time.
After Mario Goetze was denied a penalty appeal, Sahin volleyed home his second on 73 minutes.
The rout was wrapped up when 19-year-old Leonardo Bittencourt scored his first Bundesliga goal, two minutes after coming off the bench, on only his second league appearance, on 78 minutes when he tapped home a Lewandowski cross.
Schalke were hammered 3-0 at Nuremberg to drop down to fifth in the league and out of the Champions League places, having been dumped out of Europe's top domestic competition with a home defeat to Galatasaray on Tuesday.
Ex-Dortmund midfielder Markus Feulner put Nuremberg ahead before Alexander Esswein converted a pass from Japan's Hiroshi Kiyotake for the hosts second as the Japanese star again provided the final pass for Mike Frantz to score the third.
Relegation-threatened Augsburg picked up their fourth win in their last 10 games to keep their survival hopes alive with a 1-0 win at Hamburg, seventh, but the Bavarian team remains five points from safety at the bottom.
Werder Bremen midfielder Aaron Hunt converted two second half-penalties to give his mid-table team a point in their 2-2 draw at bottom side Greuther Fuerth.
On Sunday, fourth-placed Eintracht Frankfurt are home to VfB Stuttgart, who are just one place above the bottom three, while mid-table Borussia Moenchengladbach host Hanover 96.
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Eintracht Frankfurt ended 521 minutes without a goal, yet were left without points in their sixth winless match in a row, when the newly promoted team lost 1-2 (1-0) at home against VfB Stuttgart. Later Borussia Mönchengladbach took another step towards European football by beating hannover 96 1-0 (1-0).
German champions Borussia Dortmund routed Freiburg 5-1 on Saturday to provisionally trim runaway league leaders Bayern Munich's lead at the top of the Bundesliga to 20 points.
Although they will face Juventus in the Champions League quarter-finals, Bayern are looking to bounce back from their 2-0 last 16, second leg defeat at home to Arsenal on Wednesday at Bayer Leverkusen on Saturday night.
Bayern Munich are just two wins from the Bundesliga title after their 2-1 victory at Bayer Leverkusen on Saturday allowed them to stay 20 points clear at the top of the table.
They have won 21 of their 26 league games this season and now only need to beat Hamburg at home next Saturday, then win at Eintracht Frankfurt on April 6 to have their 23rd German league title confirmed.
Bayern are also eyeing the Champions League title. Despite losing 2-0 to Arsenal on Wednesday, they still reached the quarter-finals on away goals to face Juventus.
With captain Philipp Lahm, wing Thomas Mueller and striker Mario Mandzukic all rested for the trip to Leverkusen, Germany forward Mario Gomez showed his strength with the opening goal on 37 minutes.
Leverkusen, the only team to beat Bayern in the Bundesliga this year, pulled a goal back when Simon Rolfes scored from a corner on 75 minutes.
But Bayern took the three points when Bastian Schweinsteiger's free kick deflected off Leverkusen's Philipp Wollscheid shoulder into his own net on 87 minutes.
Second-placed Dortmund, who play Malaga in the last eight in Europe, ran riot at Signal Iduna Park with Poland's Robert Lewandowski and Turkey's Nuri Sahin both scoring twice.
Striker Lewandowski set a new club record having now scored in each of his last eight league games, while ex-Real Madrid and Liverpool midfielder Sahin scored his first two goals since returning to Borussia in January from Anfield.
Having fallen behind to an early Jonathan Schmid goal, Dortmund grabbed the game by the scruff on the neck to flatten Freiburg with three goals in five minutes at the end of the first half.
"I can imagine Freiburg are disappointed, you wouldn't have thought this result was possible at ten minutes past four," admitted Dortmund coach Jurgen Klopp as his side took control after Freiburg dominated the first 40 minutes.
"Freiburg were very robust and tactically very good in the first half, but my team reacted by playing some very good football."
Lewandowski opened the floodgates when he broke Timo Konietzka's club record from 1964/65 with his eighth goal in consecutive league games on 41 minutes.
But the Poland star is well short of Gerd Mueller's Bundesliga record of a goal in 14 consecutive games for Bayern Munich.
Having provided the free-kick for Lewandowski to head home the first, defensive midfielder Sahin then slammed home a goal of his own on 44 minutes before Lewandowski added his second in the first minute of stoppage time.
After Mario Goetze was denied a penalty appeal, Sahin volleyed home his second on 73 minutes.
The rout was wrapped up when 19-year-old Leonardo Bittencourt scored his first Bundesliga goal, two minutes after coming off the bench, on only his second league appearance, on 78 minutes when he tapped home a Lewandowski cross.
Schalke were hammered 3-0 at Nuremberg to drop down to fifth in the league and out of the Champions League places, having been dumped out of Europe's top domestic competition with a home defeat to Galatasaray on Tuesday.
Ex-Dortmund midfielder Markus Feulner put Nuremberg ahead before Alexander Esswein converted a pass from Japan's Hiroshi Kiyotake for the hosts second as the Japanese star again provided the final pass for Mike Frantz to score the third.
Relegation-threatened Augsburg picked up their fourth win in their last 10 games to keep their survival hopes alive with a 1-0 win at Hamburg, seventh, but the Bavarian team remains five points from safety at the bottom.
Werder Bremen midfielder Aaron Hunt converted two second half-penalties to give his mid-table team a point in their 2-2 draw at bottom side Greuther Fuerth.
On Sunday, fourth-placed Eintracht Frankfurt are home to VfB Stuttgart, who are just one place above the bottom three, while mid-table Borussia Moenchengladbach host Hanover 96.
The match on Friday (8.30 pm cet):
VfL Wolfsburg - Fortuna Düsseldorf 1-1 (0-1)
The matches on Saturday (3.30 pm cet):
Borussia Dortmund - SC Freiburg 5-1 (3-1)
Werder Bremen - SpVgg Greuther Fürth 2-2 (0-0)
1. FC Nürnberg - Schalke 04 3-0 (1-0)
1899 Hoffenheim - FSV Mainz 05 0-0
Hamburger SV - FC Augsburg 0-1 (0-1)
The match on Saturday (6.30 pm cet):
Bayer Leverkusen - Bayern München 1-2 (0-1)
The match on Sunday (3.30 pm cet):
Eintracht Frankfurt - VfB Stuttgart 1-2 (1-0)
The match on Sunday (5.30 pm cet):
Borussia Mönchengladbach - Hannover 96 1-0 (1-0)
