Sandy Baltimore celebratesGetty Images
At a glance
West Ham manager Rita Guarino was in charge of her first match.
Chelsea were 4-0 up at half-time thanks to goals from Lauren James, Alyssa Thompson, Sandy Baltimore and an own goal from Yu Endo.
Baltimore added a fifth from the penalty spot in the second half.
England goalkeeper Hannah Hampton made her first start since injury.
Emma Sanders
BBC Sport women’s football news reporter at Kingsmeadow
Chelsea began the new year with an impressive victory over West Ham in visiting manager Rita Guarino's first match in the Women's Super League.
With ground to make up in the WSL title race, Chelsea put down a marker with a ruthless display at Kingsmeadow, going 4-0 up at half-time.
The defending champions, who trail league leaders Manchester City by six points, needed just 49 seconds to take the lead when Yu Endo diverted Ellie Carpenter's cross into her own net.
It was the worst possible start to life at West Ham under Guarino, who joined the club in December having previously managed in her native Italy.
Things did not improve for the Hammers who continued to give away cheap opportunities as goalkeeper Kinga Szemik's error was capitalised on by Lauren James, before Alyssa Thompson and Sandy Baltimore added to the tally.
France international Baltimore scored her second from the penalty spot after the break when West Ham striker Viviane Asseyi was deemed to have blocked a shot with her arm in the box.
West Ham sacked former boss Rehanne Skinner after eight defeats from their opening 11 matches but hopes of a dream start under Guarino were quickly dashed.
It was a humbling for second-bottom West Ham, who are desperate to move up the table, but it was always going to be a giant task to compete with Chelsea.
For the Blues, it was the perfect way to kickstart 2026 - a reminder to their rivals that they remain hot on the heels in the WSL title race.
More to follow.
Chelsea analysis: Champions back to business
Chelsea's start to the season was not as smooth as they would have liked given their dominance over the WSL in recent years.
So to end the year with a 9-1 thrashing over Liverpool and begin 2026 with an enjoyable 5-0 win over West Ham, would have pleased supporters greatly.
Bompastor's side are used to competing on all fronts having wrapped up the domestic treble and gone unbeaten last season and they usually peak after Christmas.
With Kerr continuing to build her fitness following return from injury and James involved from the start again, Chelsea's attacking options are deepening.
In previous games they have lacked ruthlessness – something Chelsea have had in abundance during their six-year stranglehold of the WSL – but there was no question of that here.
West Ham's mistakes were pounced upon immediately and Chelsea did not take their foot off the gas, piling on the pressure throughout a rampant first half.
Baltimore's first goal was the pick of the bunch as she brought a long ball down brilliantly to cut inside, then rifled her shot into the top right corner.
Chelsea will face tougher opponents over the next few months but this performance will not have been a welcome sight for their WSL title rivals.
What's next for both teams?
Chelsea are at home to Crystal Palace in the Women's FA Cup fourth round on Saturday, 17 January before travelling to Manchester City for a League Cup semi-final on Wednesday, 21 January.
They are next in WSL action on Saturday, 24 January in another big match against Arsenal.
West Ham travel to Newcastle for their FA Cup tie on Friday, 16 January and return to the WSL on Sunday, 25 January when they face Leicester City at the King Power Stadium.
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Chelsea
West Ham United
Starting XI
24H. Hampton
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5V. Buurman
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4M. Bright
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16N. Girma
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17S. Baltimore
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8E. Cuthbert
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10L. James
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6S. Nüsken
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2E. Carpenter
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12A. Thompson
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19J. Rytting Kaneryd
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18W. Kaptein
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20S. Kerr
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32L. Potter
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11G. Reiten
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42C. Sarwie
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Starting XI
1K. Szemik
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29V. Hanshaw
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13E. Nyström
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2Y. Endo
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7I. Belloumou
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22K. Gorry
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4O. Siren
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23F. Morgan
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9R. Ueki
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20V. Asseyi
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19S. Martinez
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21S. Brasero-Carreira
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15A. Csiki
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77S. Piubel
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27L. Wandeler
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