After winning their opening games, three points for either side would have made them outright Group H leaders and put them in pole position for a last-16 berth.
As it is, they will have to endure an anxious wait for the result of Poland and Colombia's clash later on Sunday to know what they need to do in the final round of fixtures on Thursday.
Eiji Kawashima was slow to react to Juan Quintero's goal for Colombia in Japan's opening 2-1 win and the goalkeeper was again at fault for Sadio Mane's early opener, punching against the forward's leg when it looked easier to catch.
His blushes were spared 11 minutes before the interval, though, when Takashi Inui whipped superbly into the bottom far corner from just inside the penalty area.
Moussa Wague thought he had snatched all three points for Aliou Cisse's side in the 71st minute, but substitute Keisuke Honda ensured a share of the spoils with a close-range finish 12 minutes from time.
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Senegal started with a spring in their step and were rewarded with the opening goal after 11 minutes, albeit in fortuitous circumstances.
Genki Haraguchi's weak headed clearance fell kindly to Youssouf Sabaly, whose tame shot was inexplicably punched against Mane's shin by Kawashima inside the six-yard box.
The Liverpool forward knew little about it, but watched on in delight as the ball nestled in the corner for his first World Cup goal.
Japan had scarcely posed a threat during the first half, but they pulled level with their first clear sight of goal after 34 minutes.
Yuto Nagatomo controlled a long ball inside the left of the area before finding Inui around 15 yards from goal, the Real Betis forward whipping a fine right-footed strike into Khadim N'Diaye's bottom corner.
Senegal should have restored their advantage six minutes before the interval when M'Baye Niang latched onto Badou Ndiaye's through ball. The striker's rushed half-volley was too close to Kawashima, though, who was able to push way to safety.
Yuya Osako squandered a glorious opportunity to put his side ahead on the hour, somehow failing to make any contact with Gaku Shibasaki's cross from just six yards out.
Inui then came agonisingly close to scoring his second of the game four minutes later when his wonderful curled effort from a surging break bounced off the crossbar.
Those missed opportunities were brought into sharp focus after 71 minutes when Wague steamed in at the back post to meet Sabaly's low cross and crash a powerful strike into the roof of the net.
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Senegal's hopes of all but securing their last-16 spot were dashed after 78 minutes, though, as Inui took full advantage of N'Diaye's missed punch to tee up Honda, who drove home from eight yards to keep Group H very much alive.
Photo Getty Images. Caption: Keisuke Honda celebrates his goal for Japan