England's 2-1 defeat to Italy in their opening game of last year's World Cup set the tone for a disappointing campaign for Roy Hodgson's men, crashing out ignominiously at the group stage.
And, after Graziano Pelle scored a 29th-minute header in Turin, England looked set to be heading for another defeat at the hands of the Azzurri.
Italy coach Antonio Conte had his own point to prove having been subjected to death threats for the alleged role played by his training methods in a knee injury suffered by Juventus midfielder Claudio Marchisio - later found to be not as serious as first thought.
However, the match was to end in disappointment for the ex-Juve coach on his old stomping ground, as Townsend's thunderous 79th-minute strike from the edge of the area extended England's unbeaten run to nine matches.
Eder and Harry Kane were rewarded for their debut goals at the weekend with starts for Italy and England respectively, but it was Marco Parolo who got the first sight of goal after 10 minutes - forcing Joe Hart to tip over his crossbar with a dipping effort from 20 yards.
Brazil-born Eder's inclusion in the squad had been the subject of fierce debate in the build-up to Sunday's 2-2 Euro 2016 qualifying draw in Bulgaria and, while he scored a vital equaliser in that clash, his first real contribution on home soil was to nearly find the corner flag with a free-kick from a promising position.
Phil Jagielka slid in to deny the Sampdoria frontman in the six-yard box moments later, before Wayne Rooney, who struck the woodwork twice in Saturday's 4-0 demolition of Lithuania, saw an effort from the edge of the box deflected against the crossbar.
Rooney then found Theo Walcott with a sublime long-range pass, but the Arsenal winger was unable to make the most of the opportunity, as the ball wound up in the arms of Gianluigi Buffon - a starter when England last visited Turin in 2000.
However, after the visitors had shown signs of promise at one end, Giorgio Chiellini danced past a ponderous Phil Jones at the other and chipped the ball into the box for Pelle to glance home.
Chris Smalling left the field injured before half-time and the England defence came under pressure at the beginning of the second - Eder drawing a good save from Hart before Pelle drilled wide.
Kane struggled to make an impact on his full international debut and saw his best effort deflected wide, before Rooney fired straight at Buffon.
Substitutions by both coaches interrupted the flow of the match in the second half, but one of those replacements, Townsend, rifled in the equaliser from 20 yards to rescue a draw for the visitors.
