Hertha, meanwhile, have won just one of their last eight league matches, but did earn a creditable 0-0 draw at Bayer Leverkusen last weekend.
Indeed, Bruno Labbadia's side displayed an unusually disciplined defensive performance at an in-form Leverkusen side who had won eight of their previous nine matches in all competitions.
Peter Bosz's side were restricted to only two shots on target in the match, with Kerem Demirbay and Leon Bailey forced to take long distance shots from range which were both comfortably saved by goalkeeper Alexander Schwolow in a first half which never really got going for either side.
Having conceded 18 goals in their first eight league matches, including five in the second half alone of the home defeat to Borussia Dortmund the previous weekend, Labbadia had clearly set his side up to be more compact and it worked extremely effectively, with substitute Jessic Nkgankam almost turning one point into three with an injury-time header.
Hertha will certainly need to be defensively resolute on Friday against their city rivals, who simply cannot stop scoring at the moment, with 13 goals in their last four Bundesliga matches.
Indeed, it has been a remarkable campaign so far for Urs Fischer's side, who are only competing in the Bundesliga for the second season in the club's history having comfortably survived relegation last time out.
Max Kruse is proving to be one of the best summer transfer window signings in Europe, with the 32-year-old surely close to an international recall having scored six and assisted five goals in only seven starts for his new club to help fire them into the Europa League qualification places.
Kruse was in superb form once again last weekend, scoring a sensational 80th minute equaliser in the 3-3 draw against Eintracht Frankfurt. The amount of swerve and power in his strike left Kevin Trapp absolutely no chance, unlike for Robert Andrich's opener when the Germany goalkeeper spilled Marcus Ingvartsen's cross into the midfielder's path for an easy tap in.
Without another inspired performance from Andre Silva, who bagged a first-half brace to level proceedings at the break after Kruse's penalty had made it 2-0 after only five minutes, Union Berlin may well have recorded their fourth successive victory. However, having remained unbeaten since the opening day, Fischer's side now have the chance to move into third position with a win across Berlin on Friday night.
Hertha Berlin Bundesliga form: LLDWLD
Union Berlin Bundesliga form: DDWWWD
Summer signing Jhon Cordoba is likely to remain injured until the New Year with a ligament issue sustained in the win at Augsburg last month, but otherwise Labbadia appears to have no injuries or suspensions to contend with.
He is unlikely to make any alterations to the XI which performed solidly at Leverkusen last weekend, with top goalscorer Matheus Cunha perhaps provided with more positional freedom to roam inside from the left flank.
Fischer, meanwhile, remains without the trio of Joel Pohjanpalo (ankle), Christian Gentner (muscular), Anthony Ujah (knee), and like Labaddia is unlikely to make any changes to his side from last weekend's draw with Frankfurt.
That would mean another start for Taiwo Awoniyi, on loan from Liverpool, in attack after the 23-year-old impressed in recent weeks by scoring in the win at FC Koln before winning the penalty from which Kruse converted against Frankfurt.
Hertha Berlin possible starting lineup:
Schwolow; Pekarik, Boyata, Alderete, Plattenhardt; Darida, Stark, Guendouzi, Cunha; Lukebakio, Piatek
Union Berlin possible starting lineup:
Luthe; Trimmel, Friedrich, Knoche, Lenz; Promel, Andrich; Becker, Kruse, Ingvarsten; Awoniyi
We say: Hertha Berlin 1-1 Union Berlin
Hertha looked like they were back on track against Leverkusen, although they will be expected to have more of the ball at home to their city rivals, who are equally content counter-attacking at will.